While Senate Republican leaders work to whip enough votes for their Obamacare repeal bill, the White House and its allies have been meeting with potential primary challengers to one of the GOP caucus’ most vulnerable senators, Jeff Flake of Arizona, according to a Monday report in Politico.

Trump himself has spoken to Jeff DeWit, the Arizona state treasurer and former Trump campaign aide, who is considering a Senate bid, two sources told Politico. White House officials have also talked to former state Sen. Kelli Ward, who challenged Sen. John McCain (R-AZ) in his primary last year and has already announced a primary challenge to Flake, and met with potential primary challenger and former Arizona Republican Party Chairman Robert Graham, according to the report.

David Bossie, a former Trump campaign aide who runs Citizens United, told Graham that conservatives were likely to back either him or DeWit in a primary with Flake, three unnamed sources told Politico.

Flake has aired criticism of Trump before, calling on him to drop out of the presidential race after the notorious “Access Hollywood” tape and questioning his decision to fire James Comey as FBI director.

Read Politico’s entire report here.