Susan Collins not only won re-election Tuesday; she became the most important member of the Senate. While this assessment, from an editor at Congressional Quarterly, may be a bit overwrought, Sen. Collins is among a shrinking group of moderate Republicans who will play crucial roles in determining what legislation moves forward and how it is shaped.

In an election when Democrat Barack Obama won every county in Maine except Piscataquis and voters elected Democrats Mike Michaud and Chellie Pingree to Congress by large margins, Sen. Collins stands as an exception. She defeated Tom Allen, a six-term representative from Maine’s 1st Congressional District with 61 percent of the vote to his 39 percent. She prevailed in every county, winning her native Aroostook County nearly three-to-one and Penobscot County by more than two-to-one. The only large communities where Rep. Allen collected more votes were his hometown of Portland, neighboring South Portland and Waterville.

She was the only Republican elected to federal office in New England.

Sen. Collins attributes her win to the fact that Maine voters value moderation, independence and hard work. They expect her to work with her colleagues, no matter their political persuasion, to do what is best for Maine and the country.

That is why Sen. Collins is so crucial, Katherine Rizzo wrote in her online column for Congressional Quarterly. “Among the Republicans re-elected this week, she is the true swing vote – the one that means the difference between a bill that moves well across the Senate floor and a bill that stumbles around with a foot stuck in the spittoons that decorate the place,” she wrote.

When Republican leaders in the Senate count votes before a bill comes to the floor or are deciding whether to filibuster others, their first consideration must be what they expect from “the ladies from Maine,” as Ms. Rizzo called Sen. Collins and fellow moderate Olympia Snowe.

The moderate group appears to have shrunk as Oregon Sen. Gordon Smith looks to have been defeated by Democrat Jeff Merkley. In Minnesota, Norm Coleman had a 727-vote lead over comedian Al Franken out of nearly 3 million votes cast, triggering an automatic recount.

“How Sens. Collins and Snowe and fellow outcasts from their party’s conservative wing behave will help determine President-elect Barack Obama’s success in moving his agenda through Congress,” Ms. Rizzo wrote. “So Ms. Collins does have an outsized dose of power.”

Sen. Collins will continue to be central to work on homeland security, Iraq strategy, financial regulations, energy policy and other issues. But, she’d better add a couple chairs to her office for all the bipartisan discussions expected to happen there.