Alan Dershowitz said Wednesday it was a "terrible mistake" if President Trump ordered the Justice Department to investigate two of his political enemies: Hillary Clinton and former FBI Director James Comey.

According to the New York Times, White House counsel Don McGahn rebuffed the president and warned him that such an order could trigger serious consequences, including impeachment.  

On "Fox & Friends," Dershowitz, a Harvard Law professor emeritus, warned about the danger of weaponizing political differences.

“It’s just each side trying to weaponize anything they can find and criminalize. You don’t like what [somebody] did in America today politically? 'Oh, let’s prosecute and go after them. Lock her up. Impeach.' That’s not the way to go," Dershowitz said. 

"If you don’t like what people have done, run against them. Use political weapons. Do not use the criminal justice system."

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Dershowitz also said Trump and his legal team were smart to submit written answers to questions from Robert Mueller, because the special counsel was "clearly" trying to spring a perjury trap with a proposed in-person interview.

Trump told Chris Wallace on "Fox News Sunday" that he probably would not sit for an in-person interview with Mueller, amid fears voiced by his attorneys that the could be tricked into a perjury trap.

Dershowitz said by providing carefully worded written answers -- vetted by the president's legal team -- this is a "win" for Trump as far as any kind of legal or impeachment vulnerability.

"Remember [a] perjury trap is a trap for the innocent as well as the guilty. You can testify completely honestly. All the prosecution needs is one witness to contradict you. If that witness is believed by the prosecutor, you have fallen into the trap," Dershowitz said.

He noted that the answers sent to Mueller were related to Russian election meddling and possible collusion between Moscow and the Trump campaign, not obstruction of justice and Trump's firing of former FBI Director James Comey.

"From day one, I have been saying on this show, the president should not answer questions about how or why he exercises constitutional authority," Dershowitz said. "So he was absolutely right not to do that."

Watch more from "Fox & Friends" above.

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