Sen. Marco Rubio argued that President Trump’s proposed plan to declare a national emergency in order to secure the funds he needs to build a wall on the southern border was a “terrible idea.”

Speaking on Meet the Press, Rubio said he believed the use of a national emergency would set an undesirable precedent. “It doesn’t mean that I don’t want border security,” he said. “I just think that’s the wrong way to achieve it. It doesn’t provide certainty. And you could very well wind up in sort of a theatric victory on the front and then not get it done.”

On Friday, Trump revived his talk of a national emergency, as he caved and congressional leaders reached a deal to reopen the government with a three-week continuing resolution that lacked any funding for a border wall. Trump threatened that if after three weeks lawmakers failed to present a bill that included border funding, he would either declare a national emergency or force another shutdown. (The recently concluded one was the longest in history, at 35 days.)

A national emergency measure would likely be challenged in federal court, where a judge would debate what makes a “national emergency.” Rubio suggested on Sunday that he believed Trump’s plan would not stand up to judicial scrutiny, and he doesn’t appear to be alone in fretting about precedent. Sen. Roy Blunt said on Fox News Sunday that while he also wanted a border wall, “there might be a future president that I don’t agree with that thinks something else is an emergency.”

According to the Washington Post, Trump has argued to other White House officials that declaring a national emergency could pressure Congress to include wall funding in its legislative package and reassure his base that he is not giving up on his promise.