WASHINGTON -- Underdogs trying to ride a wave of anti-establishment fervor are mounting challenges to the Republican Party's hand-picked Senate candidates in several states.

The trend suggests that conservative surges in a New York House race and a Senate primary in Florida were not isolated incidents and pose a dilemma for the GOP. Party leaders have stopped endorsing candidates, and in some cases establishment candidates have shifted to the right.

Challengers are seizing on the fact that their rivals were recruited by the National Republican Senatorial Committee, the party organization that finds and vets candidates. They are presenting such links as evidence of coziness with party leaders unpopular with conservatives for supporting Wall Street bailouts and other spending programs.

In Kentucky, Rand Paul, the son of 2008 presidential candidate Ron Paul, is ahead in fund raising. He is competing with a candidate backed by Senate Minority Leader Mitch McConnell, also of Kentucky. The candidate, Kentucky Secretary of State Trey Grayson, has now taken to criticizing some of Mr. McConnell's views.

Two other NRSC recruits, former Rep. Rob Simmons of Connecticut and Rep. Mark Kirk of Illinois, have recently renounced past support for cap-and-trade legislation aimed at addressing climate change, as they reintroduce themselves as fiscal conservatives.