It's Democrats who are facing the most trouble in Tuesday's primaries. Sen. Arlen Specter is in a serious jam in Pennsylvania, and Sen. Blanche Lincoln had to move left and spend big to hold off a challenge in Arkansas.
But while there is no Republican incumbent candidate at risk, one of the GOP's incumbent ideas -- support for the occupation of Afghanistan -- is headed for a fall.
An old-fashioned whupping is shaping up in Kentucky, and Afghanistan helped stir it up.
Rand Paul, an eye surgeon who got into politics by working on the campaigns of his father, libertarian Rep. Ron Paul, is pounding Trey Grayson, a two-term secretary of state groomed for the Senate by fellow Kentuckian Senate Minority Leader Mitch McConnell.
They both label themselves as "100 percent pro-life," small-government conservatives. They are both anti-bailout, anti-Obamacare, pro-border fence and pro-gun.
But there are two major differences between Paul and Grayson.
One is stylistic.
Grayson seems to have been born a senator. A corporate lawyer from the Cincinnati suburbs, he has the look and the cautious speech common in the upper chamber.
Paul, a Texan who started practicing in Bowling Green 17 years ago after he married a Kentucky girl, looks like a small-town doctor and talks like a constitutional law professor.
In a normal year, Grayson would have the advantage. But this isn't a normal year. Disgust with Washington means Grayson's well-cultivated quasi-incumbency is no help.
The other difference is on national defense.
Paul says invading Iraq was the wrong thing to do, and while he supported the attack on Afghanistan, he expresses reservations about President Obama's mission for U.S. forces there and speaks about the need to scale back overseas commitments.
Grayson, meanwhile, defends the Iraq invasion and argues for a long-term commitment to Afghanistan as part of "keeping America on the offensive" in the war on terrorism.
Grayson hammered Paul on the difference with some nasty ads, suggesting that Paul had blamed America for the Sept. 11 attacks because he had argued that previous American policies had helped galvanize Islamists.
The Grayson strategy was to tie Paul to the "truther" movement that holds that Sept. 11 was an act of mass murder perpetrated by the Bush administration.
That's how Grayson won the backing of former Vice President Cheney and former New York Mayor Rudy Giuliani, who bashed Paul just as he had derided Paul's father in the 2008 Republican primaries.
Pundits expected Paul's insurgent candidacy to fizzle.
Kentucky is a state of 4.3 million people that boasts more than 400,000 veterans and 36,000 active-duty military members on two big bases: the elite 101st Airborne Division at Fort Campbell and the army's tank training center at Fort Knox.
But Paul hit back hard. His response ad used images from the Sept. 11 attacks and said "fighting back was the right thing to do." He then spoke directly to Grayson, saying "your shameful TV ad is a lie, and it dishonors you."
His message on the stump was that he wanted America have the most powerful military in the world as a deterrent to our enemies, not to be a policeman or a community organizer to failed nations.
It's the same message that worked for candidate George W. Bush in 2000 and a common thread of conservative foreign policy until Bush embraced an interventionist approach after 9/11.
Grayson's slimy ad and Paul's rejoinder helped Paul get the endorsement of Sarah Palin and the man he seeks to replace, retiring Sen. Jim Bunning.
Since committing to a second troop surge in Afghanistan last fall, Obama has enjoyed the support of most Republicans for his plan.
But as U.S. troop levels there approach 100,000, voters are hearing more about NATO medals for "courageous restraint," rules of engagement designed to make American troops targets and politically correct language that turns an "attack" into a "combat operation," which then becomes simply "a process."
Establishment Republicans have been quick to embrace small-government rhetoric this year. When you've had a 106 percent increase in the federal budget since 2000, that part's easy.
It's been harder, though, for McConnell's set to give up the idea of Wilsonian interventionism that the GOP took to heart during the second Bush term.
If Paul pummels Grayson in an election that has given the fullest airing yet to the conservative split on the activist foreign policy of the Bush years, expect to see more Republicans expressing their reservations about Obama's Afghan policy.
Chris Stirewalt is the political editor of the Washington Examiner. He can be reached at email@example.com.