UPDATE 9 a.m.: Maine Senate President Kevin Raye will continue his challenge against Mike Michaud in the 2nd Congressional District and will not seek the Senate seat, according to a statement sent out Friday morning.

AUGUSTA, Maine — Rep. Mike Michaud announced late Thursday that he would not run for the U.S. Senate seat now held by Olympia Snowe and instead would focus on seeking re-election to the U.S. House.

“I want to continue to represent the wonderful people of Maine’s second district and keep working on the unique issues and challenges we face,” Michaud said in a statement sent out about 9 p.m. “I am also very proud of what I have been able to accomplish on behalf of Maine’s and America’s veterans and that work must continue.”

“I join many Mainers in being frustrated with how Washington operates and believe that both sides of Capitol Hill have fallen into a partisan rut. However, I am proud of being able to work across the aisle to deliver results and I think, for now, I can best continue those efforts in the House.”

Michaud’s decision likely paves the way for one of two Democrats — U.S. Rep. Chellie Pingree, who represents Maine’s 1st District, and former two-term Gov. John Baldacci — who have both started gathering signatures for the Senate race.

His decision also could help determine which Republicans or independents decide to enter the race.

As Michaud, Pingree and Baldacci wasted little time in taking the first step to run for the U.S. Senate, state Republicans appeared to be exercising caution in that race.

Many top-tier GOP names are being discussed but they have not officially begun gathering signatures as of late Thursday, according to elections officials. Neither have prominent independents such as former Gov. Angus King or Eliot Cutler.

Party candidates only have until March 15 to turn in 2,000 signatures to run for the seat unexpectedly being given up by Snowe.

So what are Republicans waiting for?

“Republicans are more thoughtful in our policies and our politics,” said Brent Littlefield, a GOP strategist and a senior adviser to Gov. Paul LePage.

University of Maine political scientist Mark Brewer said there is more to it than that.

“For the big-name Democrats, they are all top-tier candidates. There isn’t anyone on the Republican side with that kind of resume,” Brewer said. “I think part of the reason why all three [Democrats] came out early was: they wanted to make it clear to voters and Democratic activists that they were all interested. For the Republicans, I think it makes sense for them to wait a little bit.”

One candidate, Scott D’Amboise, is in the Senate race already, but the reality is that other Republicans could be gathering signatures quietly already.

Megan Sanborn, spokeswoman for the Secretary of State’s Office, said Thursday that candidates can request blank petitions or print petitions online and begin gathering signatures. In that instance, the secretary of state would not know the identity of a candidate until signatures are turned in.

“It’s certainly hard for us to know exactly who is gathering signatures at this point and we may not know until March 15,” Sanborn said.

That means the already long list of candidates for Senate, and also for Maine’s two U.S. House seats, could be even longer.

A handful of Democrats — House Minority Leader Emily Cain, former Secretary of State Matt Dunlap and former state senator Bruce Bryant — all took out papers this week to explore a run for the 2nd District seat. It’s not clear if any or all will remain in the race in light of Michaud’s decision.

On the Republican side, all eyes now will be on Senate President Kevin Raye, who is Michaud’s challenger in the 2nd District but also is considering entering the Senate race.

Party candidates for Senate have until March 15 to gather 2,000 valid signatures. House candidates need 1,000 signatures. Independents, however, don’t face the same tight deadline as major party candidates. For an independent to get on the general election ballot, he or she would need to gather 4,000 signatures by June 1.

Maine GOP Chairman Charlie Webster said his party’s leaders are having a lot of discussions about potential candidates but he wasn’t ready to identify anybody just yet.

“My opinion is that it will be a three-way race,” he said. “It will be one of the liberals and I think [former two-term independent Gov. Angus] King will run. That means we need to come to an agreement to bring someone that would be different than those two.”

A candidate cannot run for a House seat and Senate seat at the same time in Maine, according to Julie Flynn with the Secretary of State’s Office. In other words, if Pingree decided by March 15 to officially enter the Senate race, she would not be able to run for re-election in the House should she lose in a Senate primary.

Brewer said Thursday — before Michaud’s late announcement — that he would be surprised if both Pingree and Michaud stayed in the race. He also said he thought Michaud was the strongest Democratic candidate for the Senate.

“He’s popular in his district and I don’t think his lack of name recognition in the 1st District hurts him because he’s still a Democrat,” Brewer said. “A lot of people think Pingree is the front-runner, but I think she’s the weakest of the three. I can’t see her having an easy time getting support in the 2nd District.”

As for Baldacci, Brewer said, “He has a nice resume and he’s won a lot of campaigns but there are still some lingering negatives from his time as governor.”

Another question that has been posed is whether candidates who were gathering signatures to run for the Senate could use those same signatures to run for the House, or vice versa. Flynn said that’s not allowed.

That means someone like Raye, who has gathered the necessary signatures to run for the House, would have to start from scratch if he’s interested in running for the Senate. Brewer said a candidate like Raye has more incentive to collect signatures quietly.

“If you’re Raye, you don’t want people to see that you’re doing something strategically,” he said.

The other big unknown in the Senate race could be independent candidates, specifically King and Cutler, who finished a close second to Gov. Paul LePage in the 2010 gubernatorial election.

“I think King is stronger than Cutler,” Brewer said. “There are plenty of people who look back fondly on King and have wondered why he didn’t try to do something else.”