President Trump’s tariffs on Mexico and Canada will go into effect on Tuesday. Some GOP allies are already looking for a carveout.

Sen. Charles E. Grassley, Iowa Republican, urged Mr. Trump on Monday to look at exempting potash, or potassium-rich minerals that are critical components of fertilizer.

Mr. Grassley, writing on X, said farmers are reeling from high fertilizer prices due to “Biden inflation” so they cannot bear more pressure.

“So I plead [with] President Trump to exempt potash from the tariff because family farmers get most of our potash from Canada,” Mr. Grassley wrote.

The senator faced an immediate backlash from online commenters who said elections have consequences and he has to accept the good and the bad of his support for Mr. Trump.

It would be unfair to exempt political supporters while the rest of the U.S. economy suffers, critics said.

The White House said on Saturday Mr. Trump planned to impose a 25% tariff on goods from Canada and Mexico, plus an additional 10% tariff on Chinese goods. Energy imports from Canada will get a lower tariff of 10%.

The president said Canada and Mexico need to clamp down on illegal migration and drug trafficking and allow more U.S. products into their markets. He admitted there could be short-term pain from the levies, given higher costs along supply chains and potential higher prices at checkout.

Mr. Trump agreed Monday to delay the Mexico tariffs for one month, enthusing Mr. Grassley.

“Good news on Mexico tariff pause for 1 month. Hopefully negotiating will preempt more talk of tariffs,” Mr. Grassley wrote on X.

But he said tariffs are an effective tool for generating revenue and getting a fair shake for American workers.

While Mr. Grassley looked for a fertilizer exemption, some companies said they were well-insulated against the tariffs because their products are homemade.

“While we are a global business, our beers and beverages are generally made in the market in which they are sold, meaning the vast majority of our brands sold in the U.S. are made in the U.S. with U.S. ingredients,” said Rachel Gellman Johnson, senior director of corporate reputation for Molson Coors. “The same is true in our Canadian business as well. Our products will continue to be available nationwide in both countries.”

• Tom Howell Jr. can be reached at thowell@washingtontimes.com.