Former Gov. John Baldacci withdrew from the U.S. Senate race Wednesday, leaving the Democrats without a candidate with statewide visibility and the filing deadline hours away.

Baldacci said that he had been seriously considering running in the Democratic primary but decided late Tuesday that it would be difficult for his family if he were to return to Washington for six years.

Baldacci’s decision propels former Gov. Angus King, an independent, into clear front-runner status in the race, which could help decide the balance of power in the Senate.

The seat currently is held by Sen. Olympia Snowe, R-Maine, who decided not to seek a fourth term because of her frustration with the intense partisanship in Washington. That decision had been seen as providing a rare opportunity for Democrats to take a seat currently held by a Republican and possibly hold on to a majority in the Senate.

Sen. John Cornyn, R-Texas, chairman of the National Republican Senatorial Committee, said Baldacci’s departure suggests Democrats were trying to clear the field for King, who is seen as more Democrat-leaning than Republican.

“I think it looks like Gov. King is the Democratic Party’s choice,” Cornyn said in an interview on Capitol Hill.

Jennifer Duffy, a senior editor at the nonpartisan Cook Political Report in Washington, said that the decision by Baldacci “changes the outlook of the race without a first-tier Democrat.”

Still, while it would seem to increase King’s chances of winning, the absence of a top Democrat in the race also increases the pressure on King, she said.

“Voters of both parties, but now especially Democrats, are going to want to know which party King will caucus with” if he wins the Senate seat, Duffy said.

King has said he won’t say whether he will caucus with Democrats or Republicans until he goes to Washington. Maine’s available seat could determine the balance of power in the Senate as Democrats try to hold on to their 53-47 majority this fall.

Nathan Gonzales, deputy editor of the nonpartisan Rothenberg Political Report in Washington, said “Democrats will have a candidate on the ballot in Maine this fall, but the nominee shouldn’t expect any help from the national party. It’s pretty clear that Democratic strategists are willing to take their chances that, if elected, King will help them stay in the majority.”

Larry Sabato, director of the Center for Politics at the University of Virginia, said he now rates King’s prospects of winning as high.

“I never call anyone ‘senator’ until the people have their say, but King is perhaps more heavily favored now for an open Senate seat than anyone in any state this year,” Sabato said.

That seems to be the view inside Maine as well.

Ethan Strimling, a former Democratic state senator and now a political analyst, said Baldacci’s decision leaves his party in a tough spot, especially after Reps. Chellie Pingree, a Democrat from the 1st District, and Mike Michaud, a Democrat from the 2nd District, considered running for the Senate but ultimately decided to seek re-election to the House.

“Two weeks ago we had three rock stars that were running in Chellie, Mike and John, and now we’re in a very precarious position,” Strimling said.

Strimling noted that in 2010, the Democratic candidate for governor, state Sen. Libby Mitchell, finished third behind Gov. Paul LePage, R-Maine, and Eliot Cutler, an independent candidate. The Democrats also lost their majorities in the state Senate and House that year, he said.

“You need somebody at the top of the ticket to really be the standard bearer for the party,” he said. Those left in the race, he said, lack the stature to raise a lot of money for the race and possibly lift others in the party running for the Legislature.

“We could be confronting irrelevancy,” Strimling said of the Democrats.

He said the failure of a prominent Democrat to jump in quickly left a vacuum for King to fill. After he got into the race, Strimling said, a top Democrat who decided to run could be seen as a spoiler who was willing to risk repeating the fates of Mitchell and Cutler, who split moderate and liberal votes, allowing a Republican to win with a minority of the vote.

Baldacci’s decision not to run leaves Matthew Dunlap, a former secretary of state, as the only Democratic candidate to have filed papers for the seat.

State Sen. Cynthia Dill, D-Cape Elizabeth, said she would file her papers today. Benjamin Pollard, another announced candidate, said he was still circulating nominating petitions but was “optimistic” he would get the minimum of 2,000 signatures before today’s 5 p.m. deadline.

Attempts to contact state Rep. Jon Hinck, D-Portland, the other announced Democratic candidate, were unsuccessful.

Baldacci, 57, who served two terms as Maine governor and was in the U.S. House for eight years, noted that he had been working for the Defense Department on military health care issues and is eager to return to Maine when his contract for that position expires at the end of next week.

He and his wife, Karen, have a home in Holden. Their son, Jack, is a junior at the University of Maine.

“It’s time for me to come home to Maine, not to re-up for a potential six more years down in Washington,” Baldacci said. “This is the right decision for me and my family.”

Republicans Scott D’Amboise of Lisbon Falls; state Sen. Debra Plowman, R-Hampden; former state Senate President Rick Bennett; and Secretary of State Charlie Summers all have filed papers for the Senate seat. Two other prominent GOP candidates are State Treasurer Bruce Poliquin and Attorney General Bill Schneider, but they hadn’t filed papers as of the end of the day Wednesday.

Edward D. Murphy — 791-6465

emurphy@pressherald.com

Jonathan Riskind — 791-6280

jriskind@mainetoday.com

Twitter: MaineTodayDC