Fresh off his takedowns of GOP dissenters in this month's primaries, President Trump is already making a list of Republicans who could be on his 2028 chopping block. Why it matters: Trump's string of primary wins over GOP adversaries has reaffirmed his dominance over the party — and now he's looking to extend that influence after he leaves office in January 2029. What they're saying: " Do not ever doubt President Trump and his political power. F**k around, find out," White House communications director Steven Cheung wrote on X Tuesday after Trump-backed Ed Gallrein unseated Rep. Thomas Massie (R-Ky.), a frequent critic of the president. Zoom in: Massie's loss followed a weekend in which another of Trump's longtime targets — Sen. Bill Cassidy (R-La.), who drew Trump's wrath five years ago by voting to convict him for his role in the Jan. 6 riot — failed to make a runoff for the Senate seat. This week, Trump hasn't been shy about identifying possible future targets in his party: 1. Colorado Rep.…