The Democrats did not see this coming. Of course Massachusetts voters would elect a Democrat to fill the Senate seat left vacant by the death of Sen. Ted Kennedy. Isn't Massachusetts the bluest of blue states, dominated by labor unions, liberal thinkers and other core elements of the Democratic Party?

Well, yes and no. Democrats do outnumber Republicans by three to one in the state, but the biggest block of registered voters is now those with no party affiliation. And those voters could deliver a Republican upset victory in today's special election.

Polls show the race between Attorney General Martha Coakley and her Republican opponent Scott Brown, a Republican state senator, is too close to call. Concerned that the Democrat could lose the election, President Barack Obama paid a visit to Massachusetts Sunday to campaign for Coakley and try to excite the party base.

Brown does not have much of a record to defend. As a Republican in a Democratic dominated legislature, his record is one of opposition to state spending. He has not had the votes to push his own agenda forward. But his anti-government, anti-status quo position well suits the mood of the voting public.

That public is upset by the continuing economic struggles and high unemployment that, after a year in control, is now the burden of President Obama and the Democrats. People are nervous about or outright opposed to the massive health care reform bill in the Congress that has been the subject of so much insider deal making. Bailouts, massive deficits, undetected terrorists and the escalation of the war in Afghanistan all add to the electorate's sour mood.

Brown, who makes much of the fact that he drives a truck with 200,000 miles and says he knows the struggles of the middle class, is effectively tapping into that discontent. Voters can send a loud message to Washington, he argues, by electing him to the Senate. And indeed they would.

His election could kill any prospect of health care reform for years to come. The 60 Senate votes needed to block a Republican filibuster would be lost. Democrats are scrambling for a contingency for quick approval if Brown gets elected, but I suspect some moderate Democrats in the Senate will abandon the health care bill if they see a Republican win in Massachusetts.

However things turn out, the close Massachusetts' Senate race has to have Democrats very nervous about the November 2010 election.

The key today will be turnout. Members of the Tea Party Movement and other Obama critics are certainly fired up about handing the president a big defeat via a Brown victory. But can the Democrats energize their supporters as well? My guess is, given the closeness of the race and the high stakes, they will. My call? Coakley squeaks out a narrow victory.