WASHINGTON — President Donald Trump went after House Speaker Paul Ryan on Wednesday for refusing to back his idea to strip birthright citizenship by executive order.

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

On Tuesday, Ryan said Trump had no authority to strip the right of citizenship from individuals born in the United States to immigrant parents.

"Well you obviously cannot do that," Ryan said during an interview with a Kentucky radio station. "You cannot end birthright citizenship with an executive order."

"We didn't like it when Obama tried changing immigration laws via executive action, and obviously as conservatives we believe in the Constitution," he added. "As a conservative, 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."

Ryan's take on the idea that arose during an interview with Axios is along the same lines as what most legal experts and scholars believe: that ending birthright citizenship by an executive order would be unconstitutional.

"I think the 14th Amendment is clear in enshrining birthright citizenship in the law, and there is interpretive case law from the Supreme Court supporting this," Tennessee-based immigration lawyer Greg Siskin told Business Insider. "Even with a conservative Supreme Court, I have faith the Court will reject this extremist act."