The fate of President Barack Obama's ambitious reform agenda may depend on the race to succeed the late Democratic Senator Edward Kennedy.
Voters in Massachusetts vote for a new senator tomorrow in a special election following the death of Mr Kennedy.
Republican Scott Brown score is tipped for a stunning upset against Democrat Martha Coakley in what was believed to be one of her party's safest seats.
Polls currently put Mr Brown even or ahead. The latest Public Policy Polling survey conducted over the weekend gives Brown 51% to Coakley's 46%.
The stakes are huge, not so much for who will represent the northeastern state, but because a win by Brown would demolish the fragile 'supermajority' Democrats use in the Senate to override opposition to health care reform and the rest of MR Obama's agenda.
With 60 Senate votes, Democrats are able to prevent Republican filibusters and push through legislation.
With only 59, Democrats would need Republican support and that, in today's increasingly rancorous partisan divide, looks unlikely to happen.
Barack Obama showed his alarm yesterday when he took time off from the Haiti earthquake crisis and other pressing issues to campaign in Boston.
He told a noisy crowd of Coakley supporters that the big initiatives of his presidency - the health care plan, clean energy initiatives, and attempts to repair the damage from last year's financial meltdown - are on the line.
'A lot of these measures are going to rest on one vote in the United States Senate,' Obama said. 'That's why the opponents of change and progress have been pouring money in.'
Mr Obama faces this perilous situation exactly a year after his 20 January inauguration and his lofty promise to bring in a new climate of political cooperation.
Most damaging of all to the Democrats would be collapse of their bogged-down health care reform plan. The bill is said by the party to be almost ready for passing, but if that 60th Senate vote is not there, Obama's landmark initiative could die.
Democrats are racing to draw up contingency plans for a rapid passing of health care in the event of losing the Massachusetts seat, but that would likely provoke a firestorm of Republican complaints.
Equally alarming for President Obama is the potential for this special election to herald defeat in the nationwide mid-term congressional elections due in November.
