Charles Krauthammer was on “The Kelly File” tonight, where he blasted potential executive action on illegal immigration.

“It is very clear that what he’s doing now […] is a flagrant assault on the Constitution, on the separation of powers," Krauthammer said of President Barack Obama.

Krauthammer said that he’s sure Attorney General Eric Holder will be able to find lawyers who say that this action is OK.

“As we know, if you’re a district attorney, you can get a grand jury to indict a ham sandwich, and this is the equivalent,” he said.

Of this potential executive action, he said, "I believe this is an impeachable offense."

Krauthammer stressed that the GOP should oppose the executive action, but warned Republicans should not shut down the government over it. He said that Democrats who support this potential executive action will regret it.

Congress has to pass laws and Obama has to sign them, Krauthammer said.

“That’s the way the damn thing works."