Paul to Clinton: Give back Planned Parenthood money. Reuters/Carlos Barria

At an anti-abortion rally on Capitol Hill, Sen. Rand Paul (R-Ky.) called on the Democratic presidential frontrunner to refund any donations from Planned Parenthood.

"Hillary Clinton's hands are stained by accepting this money," said Paul, who says he has been guaranteed a vote to ban any taxpayer funding for the family planning group. (It currently receives funding that is prohibited from being used for abortion.) "She needs to immediately return every red cent she has received from Planned Parenthood employees."

In a statement, Paul cited research from the Washington Free Beacon to back up his five-digit Clinton cash figure. In an interview, Paul said that he was doing exactly what Republicans had been subjected to for years.

"She’s gotten over $10,000 in Planned Parenthood donations that we can find," Paul said. "My guess is that if you add up donations from people who are employed by Planned Parenthood, you'd find even more. The ones we found are prominent donors. This happens all the time on the right, where some unsavory organization gives money, and everyone says: Give it back. She ought to be asked whether she’s going to do that."

Paul told The Washington Post yesterday that he had been assured a vote on his defunding bill. That would be a large step forward for the anti-abortion cause, which has seen the defunding provision stall in the House and kept out of must-pass bills. Still, Paul was not ready to predict that his bill would get the 60 votes required for cloture.

[Rand Paul says the GOP can defund Planned Parenthood before the recess]

"You have to look at victories where you can find them," he said. "Many people have been stymied from getting a vote; now they're energized and excited. Getting to 60 is hard, maybe a bar too high for us, but we’re going to try. If we get 54 Republicans and three or four Democrats, well, that's 58 votes. We can build on that."

Paul's anti-abortion politics have been an omnipresent, if sometimes little-covered, part of his agenda. In 2011, upon arriving in the Senate, Paul introduced a bill that would have defined "personhood" as starting at the moment of conception. When a Democratic Senate pushed that aside, Paul attempted to attach it to a flood relief bill.

It's been harder for Paul to distinguish himself on anti-abortion politics in the historically crowded Republican presidential field. On Tuesday, at the Capitol Hill rally, he was joined by competitors Ben Carson and Sen. Ted Cruz (R-Tex.) -- the latter having just attacked Senate Majority Leader Mitch McConnell for not allowing a vote on a separate amendment to bar Planned Parenthood funds.

In today's interview, Paul was happy to contrast his coming vote with Cruz's fizzled protest.

"You get more with sugar than with vinegar," said Paul. "I have my agreements and disagreements with people all the time. But I do try to find the times when we can have Jeffersonian peace and commerce with all. ...This is something where the caucus is going to come together, because it's overwhelmingly pro-life, but it happens only after a lot of work."