As both the United States and Mexico anxiously await Monday – when new 5% across the board tariffs are set to be imposed on Mexican imports by President Trump – a 2020 presidential candidate and Democratic senator says he isn’t even sure if the president’s move would be constitutional.

Michael Bennet, in an interview with Rick Newman for Yahoo Finance’s “Meet the Candidate” series, noted “it’s not clear to me that he has authority to put tariffs in place.”

The Colorado senator added that Trump “is claiming some sort of emergency authority based on national security interests that I think are likely to be unconstitutional anyway.”

If Trump follows through on his threat, the tariffs on Mexico are expected to face court challenges, For one, the U.S. Chamber of Commerce said it was considering its legal options in an interview with Bloomberg shortly after the tariffs were announced.

Congressional action is the other avenue that opponents of the tariffs are considering; there has been Republican pushback against the tariffs, with Senate Majority Leader Mitch McConnell telling reporters there was not much support “in my conference for tariffs.” Sen. Bennet is on board for that effort as well, especially if opponents in the Senate have have a supermajority.

“I think if there is that veto-proof majority, we should take a vote. We should take a vote anyway. Let’s see where people stand on this,” he said.

Mexican officials have been in the U.S. this week trying to negotiate a response to Trump’s demand to deal with the surge in migrants across the southern border.

For his part, Trump tweeted “there is a good chance” that he will be able to reach a deal but, if not “Mexico will begin paying Tariffs at the 5% level on Monday!”

The full interview with Bennet will be released next week on Yahoo Finance.

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