Sen. Jeff Flake (R., Ariz.) has said he would support a Democrat over embattled Republican Senate nominee Roy Moore in Alabama. Now, Flake is putting his money where his mouth is.

On Tuesday, the Arizonan tweeted a photograph of a $100 check he wrote to the campaign of Moore's opponent, Democrat Doug Jones.

"Country over Party," reads the caption.

While most Republican senators have distanced themselves from Moore to some degree amid allegations that he made unwanted sexual advances toward teenage girls when he was in his 30s, none has gone as far in the other direction as Flake.

Flake's tweet came a day after President Trump officially endorsed Moore and the Republican National Committee resumed its engagement in the race on behalf of Moore after cutting ties with him last month, after the allegations emerged. Moore has denied the allegations and has resisted calls from Senate GOP leaders to end his campaign.

Moore responded to Flake's donation by attacking him on Twitter, disparagingly labeling him as "Pro-amnesty" and "big gov't." Flake has been a proponent of comprehensive immigration reform and free trade.

Flake, who is retiring from the Senate at the end of his current term, has been one of his party's most vocal Trump critics. But he was among a handful of Republican senators who joined Trump at the White House Tuesday for a working lunch focused on economic issues.

Jones has been airing commercials touting the Republicans who have parted ways with Moore over the allegations he is facing. He released a new ad Tuesday highlighting Alabama's other Republican senator, Richard Shelby, who has said he did not vote for Moore and instead wrote in a Republican he has not named publicly.

Moore is trying to rally the state's conservative base behind his campaign. Many local GOP officials have stood by him, even as GOP senators have called for him to step aside. Moore planned to campaign Tuesday night with Steve Bannon, Trump's former chief strategist.

The special election to fill the seat once held by Attorney General Jeff Sessions is Dec. 12. Recent polls show a competitive contest.