Tea party candidates are challenging establishment Republicans across the country this year but fewer seem likely to win that in previous elections.

Wary of challenges from the right, incumbent Republicans are courting tea party voters more aggressively and raising more money to pour into primary campaigns.

In the year's first primary in Texas, Republican Sen. John Cornyn and Rep. Pete Sessions defeated tea party opponents after spending heavily on advertising.

The only tea party candidate seen as having a good chance for a Senate victory this year is Chris McDaniel of Mississippi, who is challenging GOP Sen. Thad Cochran. Movement candidates won six Senate seats in 2010 and 2012 and several dozen House seats.