WASHINGTON  The weekend ouster of Sen. Bob Bennett, a three-term Utah Republican , represents a triumph for the "Tea Party" movement and a warning for other incumbents facing ideological litmus tests this month.

Bennett, 76, failed to make the cut Saturday at a Republican Party convention dominated by Tea Party activists and fiscal conservatives concerned about the growth of government. Instead, the 3,500 delegates sent lawyer Mike Lee, 38, and businessman Tim Bridgewater, 49, to a June 22 primary.

The senator has deep roots in his state's Mormon community and solid ratings from the American Conservative Union and the National Rifle Association, and he had the backing of fellow Mormon Republican Mitt Romney.

Bennett has, however, tried to work across party lines on health care and immigration. And, along with 33 other GOP senators, Bennett backed the 2008 bailout package that then-president George W. Bush said was necessary to avoid a meltdown of the financial system.

Party conservatives hailed his defeat.

"We think this really is a harbinger of things to come," Brendan Steinhauser, political director of FreedomWorks, one of the Tea Party-affiliated groups that opposed Bennett, told USA TODAY. "It should send a shock wave and put people on notice."

Democratic National Committee Chairman Tim Kaine called it proof that the Republican Party is now in the command of its far-right wing. "That the Tea Party would consider Bob Bennett, one of the most conservative members of the U.S. Senate, too liberal, just goes to show how extreme the Tea Party is," Kaine said in a statement.

Bennett told the Associated Press he wouldn't rule out a write-in candidacy. State law prohibits him from running as an independent. "I do think I still have a lot of juice left in me," Bennett said.

"The political atmosphere obviously has been toxic, and it's very clear that some of the votes that I have cast have added to the toxic environment."

Both parties face internal strife as activists on the right and the left push to oust establishment-backed candidates for being too centrist. Three such challenges surface in May 18 primaries:

•Arkansas. Sen. Blanche Lincoln has the backing of President Obama and former president Bill Clinton, but labor and liberal groups, such as MoveOn.org, are backing Lt. Gov. Bill Halter's Democratic Senate primary challenge.

•Kentucky. Conservatives, including Sens. Jim Bunning, R-Ky., and Jim DeMint, R-S.C., are defying party chiefs, including Senate Minority Leader Mitch McConnell, to back Rand Paul, the son of libertarian Rep. Ron Paul of Texas, for the GOP Senate nomination over Secretary of State Trey Grayson.

•Pennsylvania. Sen. Arlen Specter avoided one tough primary challenge by switching from the GOP to the Democratic Party last year but now faces another. Although Obama and Gov. Ed Rendell back Specter, Rep. Joe Sestak, D-Pa., is gaining in polls with the backing of liberal groups such as Democracy for America.

Last month, Florida Gov. Charlie Crist dropped out of the Republican Senate primary in his state to run as an independent. Crist was initially backed by a number of top GOP leaders, including Sen. John Cornyn of Texas, the head of the his party's Senate campaign committee. But Crist fell far behind in the polls to former state House speaker Marco Rubio, a favorite of fiscal conservatives.

Cornyn, whose committee backed Bennett as it does all incumbents, issued a statement hailing his Utah colleague's "professionalism, integrity and friendship" and promising to "wholeheartedly" support the winner of the state's GOP primary.

The success of the conservative insurgencies will make DeMint, whose political action committee backed Rubio and Paul and endorsed Lee in Utah, more influential, predicts Steinhauser of FreedomWorks. "He took on McConnell ... and won."

Others worry that activists on the Republican right and Democratic left will purge the parties of centrists and further gridlock the Senate, where rules make action nearly impossible without bipartisan compromise.

"The parties are going through a process of purification," former senator Bob Graham, D-Fla., told USA TODAY recently. "One thing the Senate doesn't need, in my judgment, is more people who are living in the right or left end zones."