File photo shows President Barack Obama, followed by British Prime Minister Gordon Brown, center, and French President Nicolas Sarkozy, arrive to make a statement on Iran’s nuclear facility, during the G-20 summit in Pittsburg. (AP)

BOSTON (AP) – President Barack Obama will a make a last-minute campaign trip Sunday to support a Democrat who needs to win an unexpectedly close special election to fill the late Edward M. Kennedy’s Senate seat in order to keep health care reform alive.

The late-game White House aggressiveness in support of Massachusetts Democrat Martha Coakley reflected deep concern Democrats could lose the seat and with it key vote in support of the health care reform bill.

Obama wants to get a health care bill - his top domestic priority - finished before he makes a State of the Union speech to Congress early next month. The United States is the only major developed nation that does not have a comprehensive national health care plan for its citizens.

About 50 million Americans are without health insurance. With unemployment rising, many Americans are losing health insurance when they lose jobs because employers provide health care plans. ``If Scott Brown wins, it’ll kill the health bill,’’ said Massachusetts Democratic Rep. Barney Frank, referring to Coakley’s Republican opponent.

Beyond that, a poor outcome for Coakley on Tuesday would make moderate Democrats ever more nervous about backing Obama on other issues out of concern about their own re-election chances in November, undercutting his presidency just as he’s beginning his second year.

Democrats currently control just enough votes in the Senate to keep Republicans from blocking a vote in the Senate of Obama’s near-complete health care plan. If Coakley wins, she has said, she will vote, as Kennedy did, with the 57 other Democrats and two independents who side with them. Brown has made clear he would vote against the health plan, which all other Republicans oppose, giving Senate Republicans the one vote they need to block the legislation.

Secretary of State William F. Galvin, Massachusetts’ top election official, said certifying Tuesday’s results could take more than two weeks, maybe enough time for Democrats to push Obama’s signature legislation through Congress before Brown could take office. Sen. Paul G. Kirk Jr., the interim appointee to Kennedy’s seat, says he will vote for the bill if given the chance.