WASHINGTON—President Trump said he wants to sign an executive order that ends the automatic right to citizenship for anyone born in the U.S., ratcheting up his election-season remarks on immigration with a proposal many legal scholars said is unconstitutional.

In an interview published Tuesday morning, just ahead of next week’s midterms, Mr. Trump said he planned an executive order to end what is known as birthright citizenship, bypassing Congress and waving off the belief of many legal scholars that such a move would require...