On Sunday morning, Donald Trump went off on a Twitter tirade against a member of his own party.
This, in itself, isn't exactly huge news. It's far from the first time the president has turned his rhetorical cannons on his own ranks.
This time, however, his attacks were particularly biting and personal. He essentially called Tennessee Senator Bob Corker, the chair of the powerful Senate Foreign Relations Committee, a coward for not running for re-election.
He said Mr Corker "begged" for the president's endorsement, which he refused to give. He wrongly claimed that Mr Corker's support of the Iranian nuclear agreement was his only political accomplishment.