Just as the Trump administration steps up its push to move forward on tax reform, another Republican Senator has joined a rebellion that is poised to derail the president’s agenda.

Arizona Senator Jeff Flake, who has previously traded barbs with the president, said Tuesday afternoon, “Mr President, I rise today to say ‘enough,’” after declaring he will not run again. The move is not surprising considering Flake was already facing stiff opposition from the Republican base to his reelection.

Flake said in the speech to Congress that the conduct from the top of the US government was “dangerous to democracy.”

Confidence that the Senate’s narrow 52-48 majority would be enough to push through Trump’s legislative agenda was already shaken by push back from Republican Senators John McCain and Bob Corker. Corker sharpened his criticisms of the president in recent weeks, also declaring he would not run again, following McCain’s increased resistance to the president after being diagnosed with aggressive brain cancer.

Flake will now join McCain and Corker in the ranks of Republicans immune to backlash from a Republican voter base supportive of President Trump.