A Republican senator is raising concerns about the possible economic consequences of Donald Trump’s new tariffs.

Sen. Rand Paul, R-Ky., a prominent libertarian, has been one of the few voices in the GOP openly criticizing the president’s latest round of tariffs. Paul has been warning for months about the dangers of protectionist policies, first raising concerns last fall about the impact they could have on the U.S. economy.

Now, Paul is warning that the tariffs could bring political consequences as well—potentially spelling disaster for Republicans.

Speaking to reporters on Wednesday, he said that beyond disrupting markets, the tariffs have also “led to political decimation.”

When [former President William] McKinley most famously put tariffs on in 1890, they lost 50 percent of their seats in the national election,” Paul warned, according to DailyMail.com“When [Smoot-Hawley] put on their tariff in the early 1930s, we lost the House and the Senate for 60 years. So they’re not only bad economically, they’re bad politically.”

He also ripped the new tariff regime during a speech on the floor of the Senate on Wednesday, the outlet reported.

“Despite arguments to the contrary, Americans know tariffs are a tax they are going to have to pay,” said Paul. “This is a tax, plain and simple. Taxes should not be enacted by one person.”