DeMint, a South Carolina Republican, gave his support to political outsider Rand Paul, one day after Minority Floor Leader McConnell endorsed establishment candidate Trey Grayson.
"I'm endorsing Rand Paul because he's a true conservative who will stand up to the Washington establishment," said DeMint, who released a written statement saying he still supports McConnell as floor leader even though the two disagree on Kentucky's Senate race.
"Rand has been running on the issues that matter since the beginning of this campaign, DeMint said in the statement. "He's a strong advocate for balanced budgets. He wants to end the culture of earmarks. He supports term limits. And he's 100 percent pro-life. Rand is exactly the kind of leader Americans are looking for right now. He's not a career politician and he's got the guts to stand up to the massive spending, bailouts, and debt that are being forced on us in Washington.
Paul, a Bowling Green eye surgeon, and Grayson, Kentucky's secretary of state, are among five Republicans running in the May 18 primary to replace retiring U.S. Sen. Jim Bunning, the 78-year-old sports icon who opted not to seek a third term.
Bunning, who was considered politically vulnerable to potential Democratic challengers, blamed McConnell and other Republican leaders with drying up his fundraising and forcing him out of a re-election bid. When Bunning bowed out, the Republican establishment got behind Grayson. A chafed Bunning endorsed Paul, calling him "a man of integrity" and "the only true conservative" in the race.
Paul is the son of Texas congressman Ron Paul, who made an unsuccessful bid for the GOP presidential nomination in 2008. The younger Paul has capitalized on his father's political base.
Besides McConnell, Grayson has won endorsements from former Vice President Dick Cheney and former New York City Mayor Rudy Giuliani.
"I rarely endorse in primaries, but these are critical times," McConnell said in a television ad airing on behalf of Grayson. "President Obama's spending threatens to destroy more jobs. I know Trey Grayson, and trust him. We need Trey's conservative leadership to help turn back the Obama agenda."
Paul has endorsements from former Alaska Gov. Sarah Palin, former GOP presidential candidate Steve Forbes and evangelical leader James Dobson. Dobson had initially endorsed Grayson, but rescinded that endorsement on Monday, saying he had been mislead by Republican leaders about Paul's stand on abortion and other social issues.
As chairman of the Senate Conservative Fund, DeMint has endorsed several other conservative U.S. Senate candidates, including Florida Republican Marco Rubio, who, like Paul, is the tea party favorite. The PAC supports conservative candidates who are often overlooked or even opposed by the Washington establishment.
The PAC is also supporting Senate candidates Pat Toomey in Pennsylvania, Chuck DeVore in California, and Ken Buck in Colorado.