The latest Public Policy Polling survey conducted over the weekend gives Brown 51 per cent to Coakley's 46 per cent, while a poll commissioned by the Politico website showed the Republican ahead 52 to 43 per cent.
Another poll showed the two neck and neck.
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 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, which in today's increasingly rancorous partisan divide looks unlikely to happen.
The president showed his alarm Sunday 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.