Sen. Cory Gardner Cory Scott GardnerCook Political Report shifts Colorado Senate race toward Democrat Overnight Health Care: US coronavirus deaths hit 200,000 | Ginsburg's death puts future of ObamaCare at risk | Federal panel delays vote on initial COVID-19 vaccine distribution The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting MORE (Colo.), one of the Senate’s most vulnerable Republicans in 2020, is sounding the alarm to his colleagues that President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE’s tariffs will wipe out the economic benefit of the 2017 tax-reform law, which Republicans have touted as their biggest legislative accomplishment.

“The proposed tariffs will take money out of those pocket books [of Americans] and undermine the pro-growth tax and regulatory reforms at the heart of our economic boom,” Gardner wrote in a “Dear Colleague” letter Friday to the other 99 senators.

Gardner cited a Tax Foundation study reported on by The New York Times this week projecting that the lowest-earning fifth of American taxpayers would see an effective tax increase of 1.1 percent of their income this year.

ADVERTISEMENT

“According to the Tax Foundation study, the proposed tariffs on China, Mexico and Europe, among others, amounts to a ‘significant tax increase on Americans,’” he wrote to other senators.

The study also found that the middle fifth would see a 0.3 percent tax increase and that upper middle-class taxpayers would see their tax cuts from 2017 wiped out.

“Hardworking Americans are unlikely to overlook the hit to their pocket books. As the chief economist at the Tax Foundation explained, it will get ‘harder and harder for [the president] and Republicans to claim that they are cutting taxes for the middle class,” Gardner warned.

“I am all for fair trade. I am all for securing our border. But I am not for turning our backs on American workers and consumers. Nor can I turn my back on the free market truths that have made America’s economy the strongest in the world,” he wrote.

Members of both parties have furiously pushed back at Trump's protectionist trade policies toward multiple countries, including the president's threat to impose a 5 percent tariff on all imported goods from Mexico starting Monday.

Trump said Friday that there is a "good chance" that the U.S. and Mexico can reach a deal to avert the tariffs, but said they would go into effect as planned unless both sides reach an agreement on working to curb illegal immigration to the U.S.