In most states independents can gain ballot access well after the primary voting period, so they can make the threat stick: Come out against an ever-encroaching Federal government or the Tea Party candidate will get on the ballot and you can go back to your day job.
If I were advising the Democratic Congressional Campaign Committee, I would tell them to set aside a fund of money to teach Tea Party candidates how to gain ballot access in the 30 - 40 Districts which the Ds think are in most peril.
Republican challengers in Democrat districts can preempt that plot by claiming the Tea Party mantle starting, oh, tomorrow would be just about right.
Republican incumbents won't lose to Tea Party candidates. They might if they were running in a GOP primary in the Northeast, but there aren't very many Republican incumbents in that region so there is not much low hanging fruit.
The power of the Tea Baggers can be best used in weak Democratic districts where they can threaten to get on the ballot and destroy Republican chances to take back control of the U.S. House.
That is a dangerous storm bearing down on GOP hopes for November.