Perhaps more than any movement in recent memory, the tea party has changed American politics over the last two years.

But swinging control of the House and unseating some incumbents in primaries is one thing. Can the tea party actually change the nature of a presidential race?

The answer is yes – at least, to some extent. But there is also plenty of reason to believe that the tea party’s potential impact on the 2012 race is overstated.

Here’s why:

First, while midterm primaries and elections are relatively low-turnout affairs, a presidential election brings many more casual voters into the process. And say what you want about the tea party, they are not casual voters.

Exit polling on Election Day 2010 indicated that as many as 40 percent of voters supported the tea party. Polling then and now shows the larger public identifies with the tea party to a significantly smaller degree – sometimes less than 30 percent.

Now, tea party voters are still likely to be the more active voters, but if a higher percentage of the population is brought into the process, that should dilute the tea party effect.

Secondly, the Republican presidential primary is the only game in town next year, barring a rare and wholly unexpected primary challenge to President Obama. That means voters who want their voices to be heard will have only a Republican presidential primary to vote in.

Particularly in states like New Hampshire and South Carolina – which have primaries that are open to independents and, in South Carolina’s case, all voters – there should be plenty of independents and even Democrats casting ballots in the GOP contest. Even in Iowa, voters can change their party registration on caucus day. Remember Operation Chaos?

The Associated Press noted in a story this weekend that 42 percent of voters in New Hampshire are independents. In 2008, they voted much more in the Democratic presidential primary than the Republican one; this year, that is likely to change significantly, shifting the entire electorate in the GOP primary to the left significantly.

Former Rep. Vin Weber (R-Minn.), an adviser to former Minnesota governor Tim Pawlenty, said that the tea party influence will be felt more in caucuses like Iowa’s, where the activist base makes up a higher percentage of the vote.

“That’s not trivial,” Weber said. “It’s probably still the case that it will have substantial influence in Iowa and Nevada caucuses.”

Third, two years is a long time to keep a movement going. We’ve written before about the (lack of) longevity of these kinds of political movements, and there is already anecdotal evidence that tea party rallies are not what they were even a year ago, particularly the Tax Day events. (It’s important to note that this could be because it’s not an election year.)

In fact, Stu Rothenberg of the Rothenberg Political Report says he fully expects the movement to die down – though not off – by the time the 2012 primary season begins.

“I think there will be some attrition in the tea party movement over the next six to nine months,” Rothenberg said. “I’m not saying it will be 50 percent, but there will be some attrition.”

Democratic consultant Mark Putnam concurs, pointing to the anti-war movement in the latter part of the 2000s as proof that it’s hard to keep momentum going for several years.

“The realities of governing and the necessary compromises that come with it tend to frustrate some voters who expect seismic changes after elections like 2008 or 2010,” Putnam said. “Those voters will often throw up their hands at the mess in Washington and simply not vote the next time around.”

The current budget battles play heavily into that potential frustration.

Many in the tea party were unhappy with the size of the cuts to this year’s budget. With looming fights over future deficit reduction plans and the raising of the debt ceiling, there is plenty of opportunity for these voters to become even more disillusioned – much as the anti-war crowd did after having such a big impact on the 2006 and 2008 elections.

Of course, there’s always the chance that the movement could become even more active, citing the lack of progress on its pet issues. Generally, though, these things head in the opposite direction. (Again, look at the anti-war movement, which is hardly satisfied with continued involvement in Iraq and Afghanistan.)

Even if the tea party could keep its momentum through the 2012 primary season, though, it’s still unlikely that its influence on the race would be as outsized as it was in 2010. The nature of the process just isn’t as conducive to one voting bloc having such a big impact.

That is not to say that Republican presidential candidates won’t look for tea party votes and that candidates like Rep. Michele Bachmann (R-Minn.) and businessman Herman Cain can’t catch on. Indeed, those candidates may do surprisingly well, and tea partiers will remain an important vote in the primaries barring a complete collapse of the movement.

It’s just to say that the electorate that installed tea party candidates like Christine O’Donnell and Sharron Angle into the nation’s most important races isn’t going to be the same electorate that picks the GOP presidential nominee.

Washington Post polling manager Peyton M. Craighill contributed to this report.