In what could be a sign of major shift, Fox News host Tucker Carlson has offered a rare and vehement condemnation of Donald Trump, saying that the phone call with the Ukrainian president where Trump pressed for an investigation into Joe Biden was improper.

Carlson has been one of Trump’s fiercest defenders, even among the Trump-friendly on-air personalities at Fox News. Carlson regularly echoed Trump’s statements that the Russian investigation was a witch hunt and has picked up the president’s attacks on political enemies, but now appears to have split with him on the Ukrainian call.

Carlson and Daily Caller co-founder Neil Patel wrote a column for the news outlet saying there is no way to defend Trump regarding his actions with the Ukrainian president, writing that it was a corrupt action.

“Donald Trump should not have been on the phone with a foreign head of state encouraging another country to investigate his political opponent, Joe Biden,” they wrote. “Some Republicans are trying, but there’s no way to spin this as a good idea.”

“Like a lot of things Trump does, it was pretty over-the-top. Once those in control of our government use it to advance their political goals, we become just another of the world’s many corrupt countries. America is better than that.”

Carlson stopped short of backing the impeachment inquiry against Trump, but his condemnation alone came as a surprise to some political experts, since Fox News has overall been a staunch defender of the president. Carlson’s condemnation of Trump could be sign of a shift within Fox News, however, as recent reports indicate the network is in turmoil over the impeachment inquiry he faces.

As Vanity Fair reported late last month, the impeachment inquiry against Trump has started a significant battle within Fox News on how to cover the story. The report noted there is a growing sentiment within the network to move on from openly supporting the president. Even fellow Trump-backer Sean Hannity has privately admitted that the whistleblower complaint looks very bad for Trump.

The report added that Fox Corp CEO Lachlan Murdoch is considering a future at the network without backing Trump.

“In recent months, Rupert’s oldest son has been holding strategy conversations with Fox executives and anchors about how Fox News should prepare for life after Trump,” the report noted. “Among the powerful voices advising Lachlan that Fox should decisively break with the president is former House speaker Paul Ryan, who joined the Fox board in March.”