WASHINGTON A rising tide of voter anger has produced serious primary challenges in both parties this year, with Republicans facing a political revolt that could sweep away powerful U.S. incumbents like Senator John McCain.
As the long primary season begins in earnest on Tuesday, establishment Republican candidates face at least a half-dozen strong challenges in party contests to pick the candidates for November's midterm election.
Three crucial Republican showdowns in May could provide a test of the strength and staying power of the conservative Tea Party -- loosely organized activists who have rallied to demand lower taxes, reduced spending and more limited government.
Republican Governor Charlie Crist's decision last week to avoid a primary fight in Florida by running for re-election as an independent was the latest fallout from an anti-establishment voter rebellion.
Crist ducked a Republican primary fight with former state House speaker Marco Rubio, a favorite of conservative Tea Party activists who have targeted mainstream Republicans and in some cases forced them to adopt more conservative stances.
President Barack Obama's Democrats face their own high-profile ideological battles, with Senators Blanche Lincoln in Arkansas and Arlen Specter in Pennsylvania hoping to survive tough challenges from the left on May 18.
Democrats are desperately trying to hold their majorities in Congress and hope the Republican infighting can help in November, when all 435 seats in the House of Representatives and 36 Senate seats are up for grabs.
"There definitely are more primary challenges this year, particularly to Republicans, where they come from Tea Party angst about the growing size of government and deficits," said Cal Jillson, a political analyst at Southern Methodist University in Dallas.
"The level of economic worry and dissatisfaction with government has made it dangerous for incumbents, and the Republican base is particularly active," he said.
FIRST TEST IN INDIANA
The first showdown will be on Tuesday in Indiana, where Tea Party favorite Marlin Stutzman -- endorsed by conservative Senator Jim DeMint -- is challenging former Senator Dan Coats for the Republican nomination for retiring Democrat Evan Bayh's seat.
On Saturday, Republican Senator Bob Bennett faces a pack of conservative challengers at the state party convention, and polls indicate he might have a tough time surviving. Bennett, normally considered a reliable conservative, has been attacked by the right for supporting the Wall Street bailout.
Kentucky then hosts a May 18 showdown between establishment favorite Trey Grayson and Rand Paul, a doctor and son of libertarian Republican Congressman Ron Paul. He has been backed by Tea Party groups and former Alaska Governor Sarah Palin.
A win in any of those races would be a breakthrough for the Tea Party movement, which has lost in a special House election in New York and in at least eight Republican primary challenges to House incumbents in Texas.
"This is going to be the month when the Tea Party gets to prove if they are real or not," said Jennifer Duffy, an analyst of Senate and governor's races at the nonpartisan Cook Political Report.
"We really don't know yet -- but we will within the next month," she said.
One of the biggest primaries will be in Arizona on August 24, when 2008 Republican presidential candidate McCain squares off against outspoken conservative J.D. Hayworth, a former congressman.
Hayworth has pushed McCain to the right, most notably on Arizona's tough new immigration law. McCain, once a moderate on immigration, backs the law signed by Arizona Governor Jan Brewer -- another incumbent who faces a tough primary challenge from the right.
Democrats have their own big battles. In Arkansas, Lincoln is battling Lieutenant Governor Bill Halter, who has mounted a progressive grass-roots challenge to Lincoln with help from labor and advocates unhappy with her opposition to a public option in the healthcare overhaul.
Specter is being challenged by Democratic Congressman Joe Sestak, who has questioned Specter's Democratic credentials after his party switch last year -- a move Specter admitted at the time was forced by his likely inability to win a Republican primary.
(Editing by Philip Barbara)