Conservative columnist Charles Krauthammer warned Democrats they will “rue the day” they failed to even once oppose President Obama’s lawless disregard for the constitutional separation of powers, noting his actions establish a precedent a Republican president will one day exploit.

Krauthammer spoke on a Fox News panel along with The Weekly Standard’s Steve Hayes and The Hill’s A.B. Stoddard, discussing the Department of Justice’s sweeping new clemency push for thousands of non-violent drug offenders.

Krauthammer expressed tentative agreement with the initiative, but noted that yet another congressional work-around by the White House makes it clear the Obama administration is sliding into a dangerous habit.

“It’s not just that he’s negligent in executing his job,” he said. “He’s being unconstitutional. And if it becomes a habit — which it’s becoming, and that’s the problem — it’s going to establish a principle that a Republican will come into office and he will say, ‘I campaigned against capital gains taxes, so I’m going to order the FBI not to collect it.’”