"When the chips are down, when the tough votes come on the fights that matter to middle-class families around this Commonwealth, who is going to be on your side?" the president asked during a rally for embattled nominee Martha Coakley as he tried to energize his dispirited base in this Democratic stronghold. "Martha's going to be on your side."
Complete Coverage: Health Care Reform
The president also made a direct appeal to independents who are trending away from the Democrat and he assailed GOP Scott Brown. "It's hard to suggest he's going to be significantly independent from the Republican agenda," Obama said.
The unexpectedly tight race for the seat held so long by Edward M. Kennedy, in a state where registered Democrats outnumber Republicans by 3-to-1, reflects a nasty anti-establishment environment that threatens Obama's support in Congress now and heading into this fall's elections.
Brown, a little-known state senator, has tapped into voter anger and anxiety over federal spending to pull even with Coakley, the state's attorney general.
On Sunday, Brown used New England's love of its sports teams in rallying voter support in his race for Senate.
Former Boston Red Sox pitcher and World Series champion Curt Schilling and former Boston College and NFL quarterback Doug Flutie appeared with Brown at a rally Sunday in Worcester.
Brown is seeking to build on momentum from polls showing the race to fill the late Edward Kennedy's U.S. Senate seat too close to call. His rally took place just moments before President Barack Obama arrived in Boston to campaign for Democrat Martha Coakley.
Brown also was joined by a celebrity from close to home, his daughter Ayla, a former contestant on "American Idol."
Also Sunday, a panicky White House and Democratic allies scrambled Sunday for a plan to salvage their hard-fought health care package in case a Republican wins Tuesday's Senate race in Massachusetts, which would enable the GOP to block further Senate action.
The likeliest scenario would require House Democrats to accept a bill the Senate passed last month, despite their objections to several parts.
Aides worked frantically Sunday amid fears that Republican Scott Brown will defeat Democrat Martha Coakley in the special election to fill the late Edward M. Kennedy's seat. A Brown win would give the GOP 41 Senate votes, enough to filibuster and block final passage of the House-Senate compromise on health care now being crafted.
House Democrats, especially liberals, viewed those compromises as vital because they view the Senate-passed version as doing too little to help working families. The House passed its own version last year, and members assumed it would be reconciled with the Senate bill and then sent back to both chambers for final approval by the narrowest of margins.
A GOP win in Massachusetts on Tuesday would likely kill that plan, because Republicans could block Senate action on the reconciled bill.
The newly discussed fallback would require House Democrats to swallow hard and approve the Senate-passed bill without changes. President Barack Obama could sign it into law without another Senate vote needed.
House leaders would urge the Senate to make some changes later under a complex plan requiring only a simple majority, but it's unclear whether that could happen.
The plan is problematic. House liberals already are bristling over changes the Senate forced upon them earlier, and some may conclude that no bill is better than the Senate bill. Meanwhile, some moderate Democrats may abandon the health bill altogether after seeing a Republican win Kennedy's seat in strongly Democratic Massachusetts.
Still, "the simplest way is the House route," a White House aide said Sunday, speaking on condition of anonymity because Democrats have not conceded the race to Brown.
If Coakley wins, final passage of a House-Senate compromise is not guaranteed but seems likely.
But even as Obama campaigned for Coakley in Boston Sunday, top aides furiously weighed options if she loses. They include:
Acting before Brown is sworn in. Congressional and White House negoatiators could try to reconcile the House and Senate bills quickly and pass them before Brown takes office. A firestorm of criticism would follow, but some Democrats say it would be better than having no bill.
Seeking a Republican to cast the crucial 60th Senate vote. Some Democrats hope Sen. Olympia Snowe, R-Maine, might do this, but others seriously doubt it.
Start over and pass a new, scaled back health bill using a complicated process that requires a simple majority of 51 Senate votes. Several Senate aides said this was unlikely.