President Donald Trump operates on loyalty — and time and time again he has shown he is not afraid to retaliate, even when he is risking a Republican seat.

According to a recent Politico report, White House officials have met with “at least three actual or prospective primary challengers to Arizona Sen. Jeff Flake in recent weeks,” including former state Sen. Kelli Ward, who has announced her bid, as well as Trump campaign COO Jeff DeWit and former state GOP Chair Robert Graham:

At a Republican National Committee meeting outside of San Diego in May, David Bossie, Trump’s deputy campaign manager and the president of the influential conservative outside group Citizens United, told Graham that either he or DeWit would likely get substantial backing from conservatives should either enter the contest, according to three people familiar with the conversation.

This comes on the heels of another Politico report earlier this month, that Trump allegedly floated spending millions of dollars out of his own pocket to oust Flake, who has been openly critical of his presidency:

In private, Trump has spoken of spending $10 million out of his own pocket to defeat an incumbent senator of his own party, Jeff Flake of Arizona, according to two sources familiar with the conversation last fall.

Flake, a vulnerable Senate Republican up for reelection in 2018, has been vocal against Trump throughout his campaign and presidency. He refused to support Trump’s nomination, has repeatedly expressed skepticism over Trump’s alleged ties with Russia, and most recently dampened expectations on the Republican agenda, openly contradicting Trump’s desire for fast policy wins.

As the incumbent Republican candidate in Arizona, Flake will be running for one of two contentious Republican senate seats. Already, a pro-Trump primary opponent, Ward, has entered the race and attacked Flake from the right for being against the president and soft on immigration. DeWit and Graham are also considering entering the race. Flake’s office did not respond when asked to comment on reports of Trump’s primarying threats.

Republicans only have eight Senate seats to defend in the 2018 election, compared with the 25 Democrats up for reelection, and only two of them — Flake and Sen. Dean Heller (R-NV) — are seats that Democrats have a real shot at picking off. Arizona, though a state with a heavy conservative tradition, is also a state with a large Hispanic population that Democrats hope to fire up as part of the resistance.

Trump has reportedly held members’ seats over their heads. During the House’s debate over the health care bill, he told House Republicans, "I honestly think many of you will lose your seats in 2018 if you don't get this done." Now, as tensions continue to mount in the Senate over health care and a new host of Russia-related scandals develop, Trump surely isn’t pleased with critical Republican voices on the Hill.

The pro-Trump movement has already put vulnerable Republicans at risk, reportedly with Trump’s blessing

Trump, still struggling with low approval ratings, appears to care about two things: loyalty and the promise of quick policy wins.

But the working relationship between the White House and Republican senators has been strained, especially after America First, a pro-Trump Super PAC, ran an attack ad against Sen. Heller for coming out against the health bill — reportedly with the White House’s blessing, according to a report from the New York Times.

Senate Majority Leader Mitch McConnell (R-KY) and a number of Republican senators weren’t happy with the campaign, and they made a point to tell the White House that was a “beyond stupid” move:

Over the weekend, Mr. McConnell made clear his unhappiness to the White House after a “super PAC” aligned with Mr. Trump started an ad campaign against Senator Dean Heller, Republican of Nevada, after he said last week that he opposed the health care bill. The majority leader — already rankled by Mr. Trump’s tweets goading him to change Senate rules to scuttle Democratic filibusters — called the White House chief of staff, Reince Priebus, to complain that the attacks were “beyond stupid,” according to two Republicans with knowledge of the tense exchange. [...] The move against Mr. Heller had the blessing of the White House, according to an official with America First, because Mr. Trump’s allies were furious that the senator would side with Nevada’s governor, Brian Sandoval, a Republican who accepted the Medicaid expansion under the health law and opposes the Republican overhaul, in criticizing the bill.

It’s not far-fetched to think America First might simply be taking cues from the president himself, who has publicly threatened members’ seats in upcoming congressional elections if they voted against him. Flake may be asking for the same treatment.

Trump’s presidency isn’t making it any easier for vulnerable Republicans

Democrats have certain factors in their favor looking toward the 2018 midterm elections. Republicans only hold small majorities in both the House and the Senate. The Democratic base looks like it’s energized, which means it will be easier to fundraise, recruit good candidates, and get people out to vote. As Vox’s Andrew Prokop explained, the party of presidents with bad approval ratings usually does badly in the midterms, and President Trump’s rating is dismal:

Trump’s approval — currently about 43 percent on average — is well within the range of presidents who have lost 20 to 50 House seats. So if it stays around there, we should expect a rough result for him in the midterms.

Still, Democrats would need an “extraordinary amount of good political fortune to retake the Senate,” Prokop writes. “Considering how dismal the map is, the party would likely be thrilled to even maintain their current number of 48 seats. (Democrats will have a better shot at the Senate in 2020, when mostly Republican seats will be on the ballot.)”

Even so, Trump is making life very difficult for incumbent Republicans. The White House’s bungled lines on the Russia investigations have escalated tensions in Congress, and Republican milquetoast reactions are already becoming fodder for Democratic attacks. An apparent lack of interest in the actual substance of the health care bill has made any skepticism on the part of worried Republicans into an act of defiance against the president’s desire for a policy win.

In the House, pressure from the White House has already pushed congressional Republicans to vote for a bill so unpopular Democrats are saying it will cost them seats. The Senate health bill, which doesn’t have the votes to pass, is also widely disliked. If they pass it, they will have to tackle Trump’s tax plan next, which is also proving to be unpopular.

To be sure, the midterm elections are more than a year away, but Democrats are racking up their attacks.