President Donald Trump’s frustration with Kirstjen Nielsen, which boiled over Wednesday in a Cabinet meeting tirade, has been growing for weeks — stoked by associates who have privately made the case that she’s a closeted “never Trumper” who still doesn’t fully back his agenda.

Trump’s advisers have been increasingly criticizing the Homeland Security chief in private conversations with the president, arguing that she isn’t doing enough to improve border security and noting that she wasn’t a vocal Trump supporter during the campaign, three people familiar with the internal discussions told POLITICO.

As a result, Trump has come to believe that Nielsen — who considered quitting this week after the president berated her over an uptick in migrant arrests — is not focused enough on carrying out his immigration agenda, one of the people said. The president has told friends that he believes chief of staff John Kelly, with whom he has a strained relationship, foisted his deputy Nielsen upon him, according to two of the people, complaining that he didn’t know what he was getting.