Fox warns Trump: Don't testify under oath. You will get caught lying.

Donald Trump has gone back to publicly insisting he’s willing to speak to special counsel Robert Mueller under oath, but even the sycophants at Fox News know he wouldn’t survive that without perjuring himself.

Trump went from being “100 percent” willing to testify under oath in the Russia investigation to saying he might not speak to Mueller at all. Then on Wednesday night, Trump went back to promising he would be willing to speak to Mueller under oath and that he’s even “looking forward to it.”

Trump’s lawyers are already quietly worrying he might perjure himself in that setting, but the Trump fans at “Fox & Friends” are not ashamed to make that declaration out loud.

On Thursday morning, Judge Andrew Napolitano told the show’s co-hosts that if Trump is subpoenaed by the Mueller grand jury, he should plead the 5th, even though it would be “politically catastrophic.”

If Mueller can get Trump talking, Napolitano said, it would give Mueller “an opportunity to trip him up.”

“They tripped up George Papadopoulos, they tripped up Mike Flynn,” Napolitano continued, attempting to paint Trump as a potential victim. But Flynn and Papadopoulos were not just charged; they pleaded guilty to crimes.

Napolitano exposed his own false premise moments later when he pointed out that Trump’s jeopardy stems from the fact that Trump would be disadvantaged by the facts.

“He doesn’t know what they know about him, he doesn’t know what others have said under oath about him,” Napolitano said. “It is very easy for them to trip him up and get him to say something that is contradictory to what he already said.”

Co-host Ainsley Earhardt then volunteered, out loud, that it was “smart” for Trump to lie about being willing to testify, then back out of it later.

“His attorneys have been saying they want him to do it because he says he wants to do it,” Napolitano fretted. “I just hope that they don’t because this is a very, very dangerous environment.”

Napolitano is right about one thing. Trump is caught in a trap, forced to decide between voluntarily speaking to Mueller or forcing a subpoena, and a politically disastrous invocation of the 5th Amendment. The last thing Trump wants to do, though, is actually face prison time for lying.

Fortunately for Mueller, Trump has already said plenty in public to implicate himself. Trump can run from Mueller, but he can’t hide from his own self-evident obstruction.