John Yoo is a Republican lawyer who is perhaps best known for authoring the “torture memos” that legally justified former President George W. Bush’s use of torture against terrorist suspects in 2002. It was a sweeping interpretation of executive power — one that allowed the Bush-led CIA to detain suspects, some of whom turned out to be innocent, without trial and torture them with techniques ranging from waterboarding to shoving hummus into their rectums. President Barack Obama put an end to the practice within days of taking office.

But in a New York Times op-ed on Monday, Yoo argued that despite his support for torture under Bush and other executive war actions, “even I have grave concerns about Mr. Trump’s uses of presidential power.”

Yoo takes aim at several of Trump’s high-profile executive orders and actions:

“Take his order to build a wall along the border with Mexico, and his suggestion that he will tax Mexican imports or currency transfers to pay for it. The president has no constitutional authority over border control, which the Supreme Court has long found rests in the hands of Congress. Under Article I of the Constitution, only Congress can fund the construction of a wall, a fence or even a walking path along the border. And the president cannot slap a tax or tariff on Mexican imports without Congress.”

“Nor can Mr. Trump pull the United States out of Nafta, because Congress made the deal with Mexico and Canada by statute. Presidents have no authority to cancel tariff and trade laws unilaterally.”

“Even though his executive order halting immigration from seven Muslim nations makes for bad policy, I believe it falls within the law. But after the order was issued, his adviser Rudolph Giuliani disclosed that Mr. Trump had initially asked for ‘a Muslim ban,’ which would most likely violate the Constitution’s protection for freedom of religion or its prohibition on the state establishment of religion, or both — no mean feat.”

Again, this is coming from one of the prominent Republican officials who stretched the limits of executive power to include torture (or “enhanced interrogation,” as he calls it). And even he argues Trump is going too far in his use of executive power.