WASHINGTON - The rising sun bathed the U.S. Capitol in postcard-perfect light early Thursday morning as U.S. Sen. Angus King walked to work from his two-room apartment a few blocks away. Suddenly, he stopped dead in his tracks.

"Isn't this amazing?" King asked, staring up in unabashed awe at the nation's political epicenter. "I mean, this is my office! I can't believe it! I can't believe it."

Only a few hours later, he was in tears.

Emerging from a closed-door meeting with grieving parents of children lost four months ago in the Sandy Hook Elementary School shooting massacre, King dabbed repeatedly at his eyes with a tissue, an almost helpless expression on his face as he walked across his crowded -- and pin-drop silent -- temporary office suite.

Then, as if leading a funeral procession, he walked the parents down a long tunnel that connects Russell Senate Office Building to the Capitol. The Sandy Hook delegation continued on to the visitors gallery; King peeled off toward the Senate chamber, where he and 67 other senators overcame the threat of a filibuster and thus cleared the way to debate, at long last, a hotly contested package of federal gun-control legislation.

"That's the first time I ever cried on the job," said King, his eyes still moist, moments after the vote. "As I said to one of the parents on the way over, 'If I don't do another thing, I'm doing something important today.' "

Fourteen months ago, before Sen. Olympia Snowe shocked all of Maine -- and indeed the nation -- by announcing she would not seek re-election out of weariness with the partisan gridlock that has Congress in a state of near-paralysis, Maine's former two-term, independent governor had little doubt his days as an elected leader were long behind him.

Yet here he is, back in the fray in a place he last worked 40 years ago as an aide to then-U.S. Sen. William Hathaway, a Maine Democrat.

Only this time, King comes with no letter denoting party affiliation affixed to his last name. A seasoned politician, to be sure, he's at the same time a wide-eyed idealist in a place that thrives on cynicism, a man on a mission (or is it a fool's errand?) to help fix what ails the most powerful deliberative body on the planet.

Friday marked the 100th day of King's six-year term. In that short time, if a two-day visit last week was any indication, he has fast become part new kid on the block, part policy wonk, part builder of bridges across the Great Partisan Divide, part wide-eyed admirer of the larger-than-life sculptures -- starting with Maine's first governor, William King -- in the Capitol's Statuary Hall.

"If there were anyone that you had to cast, from central casting, to be a senator, that would be the guy," said Senate Majority Leader Harry Reid during an interview in his palatial office just off the Senate chamber. (Rather than sit in, King opted to wait in the reception area.)

"I think he feels pretty comfortable where he is," said Reid. "He likes what he's doing. That's important."

Reid, who actually produced a copy of King's family travelogue, "Governor's Travels," from under a pile of papers on his desk, has good reason to sing the praises of Maine's independent junior senator: King, much to Reid's relief, chose in January to caucus with the Senate's majority Democrats.

Yet the positive early reviews extend across the aisle as well.

"He's a serious member of the Armed Services Committee. I noticed that he almost never misses a hearing or a meeting," said Sen. John McCain of Arizona, the second-ranking Republican on the committee. "And I've been very impressed with him. He wants to be a senator in the Maine tradition and I think he's living up to it."

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Like many in the Senate's freshman class, King has yet to be assigned a permanent office -- he hopes to get one by midsummer.

His temporary digs, just down the hall from Snowe's old sprawling suite, consist of a small personal office flanked by an open room, no bigger than most veteran senators' outer lobbies.

There, King's staff of close to two dozen aides -- most less than half his age -- sit cheek-to-jowl amid a warren of wooden desks. To the first-time visitor, the bunker-like atmosphere feels more like a campaign war room than a hall of government.

So meager is his space that King must go searching each week for a conference room to accommodate his Wednesday-morning coffees with Mainers visiting the Capitol. Last week's gathering attracted about 30 people, ranging from a Maine People's Alliance delegation in town for an immigration-reform rally to the Little family of Lewiston -- parents Todd and Jackie, Nathan, 10, and Kristen, 8 -- on a weeklong tour of Washington.

"Dear Mr. Belleau," wrote King in a note to Nathan's teacher. "Please excuse Nathan. He was helping me make laws for the country."

"They won't keep you after school now," a smiling King assured Nathan as he signed the souvenir and moved on to talk logging, immigrants' path to citizenship and whatever other issues brought his constituents from Maine to Capitol Hill.

"I see over 100 people from Maine every week," King said as he hurried from the coffee to a Senate Budget Committee hearing on the Obama administration's nomination of Sylvia Matthews Burwell to serve as director of the Office of Management and Budget. (He wanted to ask Burwell's thoughts on reducing the deficit by driving down the cost of federally funded health care.)

The pace, particularly for a man who turned 69 on March 31, is frenetic -- half the big business of the nation, half the many and varied concerns of the people who sent him here.

In addition to budget and armed services, King sits on the Senate's intelligence and rules committees, often ducking into an anteroom during committee sessions to meet with the endless stream of constituents seeking a moment of his time.

(One such break from the budget hearing last week focused on a special grade of paper, produced by a mill in Madawaska, on which informational inserts for pharmaceutical products are printed -- the visitors sought King's support in resisting efforts to move from the hard-copy to online advisories. Another short sit-down, during an armed services confirmation hearing, was with a group of gastroenterologists.)

His posture during such visits is hardly King the esteemed senator, holding court with this or that suitor for his time or influence. Rather, he seems to reach back to his days, long before he ran for anything, as the host of Maine Public Broadcasting Network's "Maine Watch" program -- a curious interviewer seeking the facts and context behind a constituent's painstakingly prepared talking points.

"It's exhausting at times," King admitted after yet another meet-and-greet with a group of teenage girls from Maine's 4-H program. "Being that 'on' all the time, one group after another, it takes a lot out of you."

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But if the politicking occasionally wears him out, King's aides and fellow senators unanimously attest, it is the legislative work that has him behaving like a man 10 or more years younger.

"He's very interested and eager -- and not just with the talking points, but with how we get down to where the decisions are actually made," said Chad Metzler, a veteran of almost 20 years on Capitol Hill, who serves as King's legislative director. "He's one of the smartest and more erudite members I've run into ... We have high confidence that when he goes out there, he knows what he's talking about."

"He's certainly an intelligent man," said Sen. Orrin Hatch, R-Utah. "And I like that very much. There's so much infighting down here that it's nice to see somebody come here to do what he thinks is right. I couldn't be higher on him."

Like the 10 other current senators with previous experience as governors -- he recently hosted all of them, at his own expense, to a Maine lobster dinner inside the Capitol -- King often finds himself balancing the art of senatorial bonhomie with an impatience to get things done.

Concerned after six weeks on the job that the Budget Committee was spending too much time dithering on when and how to draft its version of a federal budget (an accomplishment that had eluded the Senate for four years), King decided to go ahead and build one himself.

"So we got in touch with all the people down here in Washington -- you know, the think tanks," he said. "And we had two or three long and substantive meetings to design our own budget."

Kay Rand, King's chief of staff, worried such a step might be perceived as too bold an overstep for a newcomer like King. Yet much of King's work, she notes, found its way into the spending plan approved last month in an all-night session by the full Senate -- including $100 billion for research and development and rebuilding the nation's infrastructure.

"He's brought a lot of great ideas to (the budget)," said Sen. Patty Murray, D-Wash., who chairs the Budget Committee. "He comes in, he listens, he learns, he participates, he's got great ideas. I find him a really valuable member of our committee."

Not to mention a candid critic of the status quo. At one point during the marathon budget deliberations, King asked the Republicans across the committee table: "Let me just stop and ask a question -- I'm new here. If we accept some of your amendments into the budget, are you going to support it?"

The query hung in the air for several seconds. Finally, the Republicans said no, there was no way they'd line up behind the budget with or without their amendments.

Replied King, "So what the hell are we doing here?"

That same frustration colored King's reaction to earlier negotiations over the Senate's oft-used filibuster rules -- his call for "talking filibusters" in which senators must actually hold the floor to prevent a vote was left out of what many considered a watered-down set of reforms.

"I'd call it a disappointment," King said. "I wanted to do more."

Conversely, as he waded into the hot waters of post-Sandy Hook gun legislation, King found himself roundly criticized by many gun-control advocates for not wanting to do enough: While he supports universal background checks for gun buyers, limits on high-volume magazines and outlawing "straw purchases" that put guns in the hands of convicted felons, King decided not to support calls for an assault weapons ban. He concluded, after meeting extensively with advocates on both sides, that such firearms are functionally no different than most semiautomatic hunting rifles.

That said, King lay awake Wednesday night worrying how the latter position might go over with the Sandy Hook parents the next morning.

When he finally sat down with them, he recalled, "I said, 'I've got to be honest with you. Here's where I come out (on assault weapons).' "

And?

"They said, 'That's where we are, too,' " King replied, exhaling hard to show his relief.

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The roller-coaster ride, of course, has only just begun. Exhilarating as his first 100 days have been, more than 2,000 remain before the end of his term.

And beyond that, King envisions this unexpected chapter of his life lasting not one term, but in all likelihood two.

"That is, if the voters of Maine still want me after six years," he chortled.

In other words, he could be doing this until he's 80.

To appreciate what that means, consider what King did after that draining and dramatic gun vote on Thursday: a 90-minute Intelligence Committee hearing; a taping with Sen. Tom Carper, D-Del., for the first half of King's monthly radio show on WGAN in Portland; a four-minute dash across Capitol Hill for a live interview with Chris Matthews on MSNBC; a taping for the second half of his radio show with Sen. Joe Manchin, D-W.Va.; a televised Q&A with the Bangor Daily News; a taped message for a nurses' convention he couldn't attend; a two-plus-hour dinner with staff ...

"It is literally the hardest I've ever worked in my life," King said. "A -- because of the hours, and B -- because of the intensity."

Why he would do it is no mystery to Mainers who have watched him, and mostly supported him, all these years. For a man who wears his love of history on his sleeve and now walks among the larger-than-life murals, marble statues and other tributes to centuries gone by, there simply is no better place on Earth to report each day for work.

But how King, on the cusp of 70, is doing it -- the grueling 12-hour days, the relentlessly steep learning curves, the incessant relationship-building with colleagues of all political stripes (he's already had personal visits with almost half of them) -- is as hard to fathom as that magical morning light on the Capitol dome.

Exhausted? Try exhilarated.

"I don't know what it is," mused King. "The circumstances call forth the energy."

Columnist Bill Nemitz can be contacted at 791-6323 or at: