President Trump's political operation has launched an aggressive effort to unseat Kentucky Rep. Thomas Massie, its first such effort to defeat a sitting Republican incumbent, Axios has learned.

Why it matters: By going after Massie, Trump's team is looking to put wayward Republicans on notice that they're ready to play hardball.

Massie has attacked Trump over his strike on Iran, saying on X that it was "not Constitutional," prompting the president to fire back on Truth Social that the congressman is "not MAGA."