President Donald Trump thought he had a good idea: With the flick of a pen, he could sign away the constitutional right to citizenship granted to nearly everyone who is born in the United States, in an attempt to curb illegal immigration. He was very proud of the idea.

“It was always told to me that you needed a constitutional amendment. Guess what? You don't," a gleeful Trump told Axios’ Jonathan Swan when asked about his desire to end the practice of birthright citizenship, which is based on a longstanding interpretation of the 14th amendment’s classification of all persons born or naturalized in the United States “and subject to the jurisdiction thereof” as citizens.

“It’s in the process,” Trump said. “It will happen. With an executive order.”

Not so fast, said House Speaker Paul Ryan.

“You cannot end birthright citizenship with an executive order,” the Wisconsin Republican told a Kentucky radio station on Tuesday. "We didn't like it when Obama tried changing immigration laws via executive action,” Ryan added. “I'm a believer in following the plain text of the Constitution and I think in this case the 14th Amendment is pretty clear, and that would involve a very, very lengthy constitutional process."

It’s important to note just how mild (or as Ryan would view it, diplomatic) this criticism of Trump’s strategy was. During the interview, the retiring speaker reiterated that Republicans are in “total agreement” with the president on illegal immigration and border security. And when he did differ with Trump, it was on the point of process, not explicitly coming down one way or the other whether birthright citizenship ought to be altered in the first place.

While some Republicans, such as South Carolina Senator Lindsey Graham, have long sided against the Supreme Court’s more than a century-old affirmation of birthright citizenship (arguing instead that children of illegal immigrants should not be included in the interpretation), Trump wasn’t referring to a serious legislative effort to change the Constitution. He was suggesting a brazen abuse of power.

It is unclear where the president first picked up the idea that he could erase a constitutional amendment—approved by supermajorities in Congress and ratified by two-thirds of the states—simply by declaring it so. Naturally, such an attempt would be immediately subject to a wave of legal challenges, which could lead the Supreme Court to consider the matter.

And while Trump sounded committed to the effort, at this point we don’t know whether such an executive order even exists, let alone the fine details. “So-called Birthright Citizenship, which costs our Country billions of dollars and is very unfair to our citizens, will be ended one way or the other,” he wrote on Wednesday.

Even Ryan's gentle criticism, however, was too much for the president.

“Paul Ryan should be focusing on holding the Majority rather than giving his opinions on Birthright Citizenship, something he knows nothing about!” Trump tweeted on Wednesday. "Our new Republican Majority will work on this, Closing the Immigration Loopholes and Securing our Border!”

And if there is no Republican majority in the House come next week? Well, at least Trump has someone else lined up to take the blame.