Eliza Collins

USA TODAY

President Trump dared Rep. Mark Sanford to vote against the Obamacare repeal bill last week so he could put a primary challenger against the former governor in 2018, the congressman said.

According to Sanford, White House budget director Mick Mulvaney told him, "The president asked me to look you square in the eyes and to say that he hoped that you voted ‘no’ on this bill so he could run (a primary challenger) against you in 2018," according to The Post and Courier, which first reported the story. Mulvaney, a friend of Sanford's, was a South Carolina congressman before he joined the administration.

Sanford is a member of the conservative House Freedom Caucus, a group of roughly three dozen conservative lawmakers who said they’d vote against the House bill to repeal and replace Obamacare last week because they felt it didn’t go far enough.

The Freedom Caucus’ announcement that they were against the bill, coupled with a handful of moderate members who didn’t support the legislation for other reasons, ultimately forced President Trump and House Speaker Paul Ryan, R-Wis., to pull the bill from the floor. No Democrats were expected to vote for the legislation and Republicans could only lose about 20 votes for the bill to still pass.

As negotiations went on, Sanford stayed quiet about his position on the legislation. But he had voted against it when it was marked up by the House Budget Committee.

Since the bill’s failure, Trump has aimed a significant amount of his frustration at the Freedom Caucus. On Thursday, he threatened primary challengers in a tweet.

"The Freedom Caucus will hurt the entire Republican agenda if they don't get on the team, & fast," Trump tweeted. "We must fight them, & Dems, in 2018!"

While many Freedom Caucus members had been close allies of Trump’s before the implosion of the bill, Sanford had always maintained his independence. The former South Carolina governor has been critical of Trump in the past.