SPRINGFIELD, Mass.  In most elections, a politician calling himself the Tea Party candidate would cheer Democrats, raising hopes that he would siphon votes from Republicans by attracting some of the disaffected anti-Washington, anti-Obama electorate.

But when the election is being held to fill a seat that was left vacant by the death of Senator Edward M. Kennedy, and the Tea Party candidate happens to be named Joe Kennedy, things get a little murkier.

Democrats here are concerned that some uninformed voters might confuse him for a member of the better-known, well-loved Kennedy clan, which he is not. And Mr. Kennedy’s libertarian positions make him even more of a wild card in the last days of the race: some could appeal to the right, like his call to abolish the federal Department of Education, while others could appeal to the left, like his call for immediately ending the wars in Iraq and Afghanistan.

The underfinanced, little-publicized campaign of Mr. Kennedy, 38, is not likely to get many votes on Tuesday. But if the race between the major-party candidates  Martha Coakley, a Democrat and the state’s attorney general, and Scott Brown, a Republican state senator  is as tight as some polls suggest, Mr. Kennedy could play a key role by drawing just a few percentage points from either of them.