A Republican primary today is shaping up as the biggest test yet of the Tea Party movement's political muscle and the GOP establishment.
The high-profile race in Kentucky between ophthalmologist Rand Paul, son of Texas Rep. Ron Paul, and Kentucky Secretary of State Trey Grayson is poised to become the second major Tea Party victory this month.
Grayson is backed by some of the most powerful Republicans in Washington, including former vice president Dick Cheney and Senate Minority Leader Mitch McConnell, R-Ky., who especially handpicked Grayson. But Paul, a rookie politician, is leading in nearly all the public polling and is widely expected to beat Grayson.
Paul, whose father did not win a single Republican primary in the 2008 presidential race, has two big advantages: money and manpower. As the son of a former presidential candidate, he has tapped into his father's fundraising network and, as one of the most high-profile names in the Tea Party movement, has plenty of energized grassroots activists.
He has also secured the support of another Tea Party favorite, Sarah Palin, and the retiring senator from Kentucky, Jim Bunning.
"I feel a part of the Tea Party," Paul told ABCNews.com's "Top Line" last month. "I probably was at the very first Tea Party in the country in 2007. I was also there in 2008, and the first campaign event I went to in Kentucky was a Tea Party, April 15 of last year."
If Paul wins, his victory would come on the heels of the Tea Party win in Utah earlier this month when three-term incumbent Sen. Bob Bennett was denied a place on the GOP primary ballot.
Paul has used McConnell's support for Grayson to tag him with the establishment label that no candidate wants to be wearing this cycle.
"I think most Kentucky voters want to decide for themselves," Paul said. "They don't want someone in Washington to dictate their candidate."
Even though Rand Paul is expected to win on Tuesday, Grayson's backers say Paul would be vulnerable in a general election because he wants to repeal the Patriot Act and do away with any federal role in either gay marriage or drug laws.
The anti-Paul argument was recently articulated by former New York Mayor Rudy Giuliani, who famously clashed with Ron Paul during the 2008 presidential debates.
"Trey Grayson is the candidate in this race who will make the right decisions necessary to keep America safe and prevent more attacks on our homeland," Giuliani said. "He is not part of the 'blame America first' crowd that wants to bestow the rights of U.S. citizens on terrorists and point fingers at America for somehow causing 9/11."
Sarah Palin Backs Rand Paul for Kentucky Senate
Even though Paul has been attacked by Giuliani, he has some high-profile support of his own.
Paul is backed not only by retiring senator Bunning but also by Palin, a popular figure in the Tea Party.
"He's a federalist and he wants the states to have ... more say in a lot of the issues," Palin said during a recent appearance on "Fox News Sunday."
"But nobody's ever going to find a perfect candidate. There are things that I don't agree with Rand Paul and yet his domestic policies, for the most part, I do agree with. He wants limited government. He wants the feds to start taking their hands off states' issues.
"And I respect that and I'm proud to support him, again, never finding a perfect candidate," she said. "No doubt, he disagrees with me on a whole lot of issues, but ... proud to support him and others whom I can believe in."
Even though the Republican Senate contest has captured most of the attention in Kentucky, Democrats have a competitive primary of their own in the Bluegrass State.
National Democrats have tapped Jack Conway as their preferred candidate, but Lt. Gov. Dan Mongiardo has put up a spirited fight.
ABC News' David Chalian contributed to this report.