For months, Angus King has been defined by what he is not.

Not a Democrat — although he supports the president; not a Republican — although he favors cutting federal spending and red tape; King made news for refusing to say who he would caucus with, and promised to maximize his influence by waiting until the last minute before he committed.

But on Tuesday, King will finally be defined by what he is: a member of the U.S. Senate. It’s a vitally important job — the only place in the U.S. government where a small state like Maine stands on equal footing with the nation’s centers of power. Maine has a history of electing national figures to the Senate, including the woman that King will replace, Republican Olympia Snowe. She abruptly announced her retirement this year, saying that the body had become so partisan it was dysfunctional.

Fixing that dysfunction was the animating issue of the King campaign. He argued that people were fed up with a Congress that can’t make progress on the most important issues.

So-called process arguments are not supposed to win elections, but King insisted that the voters he talked to were more concerned about fixing the way government works than any other issue.

King was blessed with weak opposition. Republican Charlie Summers, a three-time loser in congressional races, could never articulate a rationale for his candidacy. Democrat Cynthia Dill was abandoned by her national party, in the end getting most of her best support in the form of television ads and mailings cynically paid for by a Republican super PAC.

King had not run a competitive race for 18 years and for a while this summer looked unprepared for the attacks that have become standard in our politics. But when he appeared alongside his rivals in debates and released a series of ads in which he looked into the camera and spoke directly to voters, concerns about his election evaporated.

It’s no doubt that King is a superior communicator, and Mainers’ confidence in his character made him resilient to the attacks.

But now that he is going to Washington, King should use his communication skills to provide a vision for the country that goes beyond fixing the process of the U.S. Senate and say how he is going to address the problems of the nation.