After abruptly announcing tariffs on imports coming from Mexico over a migrant dispute, the White House is brushing aside the concerns of powerful Republican lawmakers – including Senate Finance Chairman Charles E. Grassley.

President Donald Trump green-lighted the import fees in an attempt to push the Mexican government to clamp down on the flow of Central and South American migrants moving through its territory toward the U.S.-Mexico border.

But Grassley, whose committee handles trade issues, issued a scathing statement Thursday night, calling the move a “misuse of presidential tariff authority and counter to congressional intent.” An Iowa Republican, Grassley has voiced concerns in the past about the trade battles hurting on farmers in his state who sell to foreign markets.

White House officials appeared unconcerned Friday that a sizable number of GOP members would break with Trump, and tried to move the focus back to immigration policy.

“Congress should actually fix the laws and we wouldn’t have this problem,” Press Secretary Sarah Huckabee Sanders told reporters when asked why American consumers and businesses should foot the bill for an immigration dispute with Mexico and other countries. “Mexico should engage with us, and we wouldn’t have to take these steps.”

Minutes earlier, during a Fox News appearance, Sanders was asked directly about Grassley’s concerns, and she was equally dismissive of his worries.

[Trump sets tariffs on imports from Mexico to deter migration]

“Look, I certainly have a lot of respect for Chairman Grassley, and we work with him on a lot of things. But at the same time, the president’s No. 1 responsibility is to protect Americans, and that’s exactly what he’s doing,” she told the network.

On a briefing call Thursday night with reporters, senior administration officials declined to discuss other potential moves against Mexico that were considered.

Grassley spelled out one idea he would pursue before tariffs.

“Trade policy and border security are separate issues. President Trump should consider alternatives, such as imposing a fee on the billions of dollars of remittances that annually leave the United States to Mexico, which only encourage illegal immigration and don’t help the U.S. economy,” the chairman said in his statement.

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“It could fund border security measures and would put economic pressure on Mexico without imposing a financial burden on U.S. consumers or harming American jobs,” Grassley said. “I’ve long supported reforms to remittance law, which haven’t become law because of opposition from big banks and other financial interests. Mexico must help get the border crisis under control and the president should use appropriate authorities to apply pressure.”

In a statement, Senate Majority Leader Mitch McConnell, R-Ky., echoed Sanders in trying to pressure Democrats “to finally get serious about meaningful action” even as he called Mexico “a vital source of our joint prosperity” and stopped short of endorsing the administration’s tariff plan.

“Any proposal that impacts this relationship deserves serious examination and I look forward to discussing this plan in greater detail with my colleagues and the administration,” McConnell said.

Administration officials were circumspect about just which members were notified before the tariffs were announced Thursday evening. But comments on that call by Mick Mulvaney, acting White House chief of staff, indicate it was a very short list.

“We were in communication with leadership in both chambers. Obviously, we talked to Republicans more than we did Democrats,” he said. The former South Carolina GOP congressman later clarified his own response — he admitted to be having trouble reading his own handwritten notes — saying White House officials talked to “zero” Democrats about the Mexico tariffs.

Mulvaney described his former congressional Republican colleagues as supportive of the move, saying he and other White House officials assuaged some concerns “regarding the authorities … and we feel like we were able to get them more comfortable with that.”

Grassley’s statement, however, suggests otherwise. So, too, did comments Rep. Peter King, Trump’s fellow New York Republican, made in a Friday morning television interview urging the White House to consider other measures.

But Trump and his team have dug in, and are as defiant as ever on the matter.

The president fired off several morning tweets defending his move, saying, “Mexico has taken advantage of the United States for decades.” He also pinned blame for the attempted border crossing uptick on congressional Democrats for passing “BAD” immigration laws – even though his own party has controlled one or both chambers of Congress since 2011, and the House for 20 of the last 26 years.

Mexico has taken advantage of the United States for decades. Because of the Dems, our Immigration Laws are BAD. Mexico makes a FORTUNE from the U.S., have for decades, they can easily fix this problem. Time for them to finally do what must be done!

— Donald J. Trump (@realDonaldTrump) May 31, 2019

In order not to pay Tariffs, if they start rising, companies will leave Mexico, which has taken 30% of our Auto Industry, and come back home to the USA. Mexico must take back their country from the drug lords and cartels. The Tariff is about stopping drugs as well as illegals!

— Donald J. Trump (@realDonaldTrump) May 31, 2019

90% of the Drugs coming into the United States come through Mexico & our Southern Border. 80,000 people died last year, 1,000,000 people ruined. This has gone on for many years & nothing has been done about it. We have a 100 Billion Dollar Trade Deficit with Mexico. It’s time!

— Donald J. Trump (@realDonaldTrump) May 31, 2019

[Trump tries to walk back claim of ‘Russia helping me to get elected’]

White House aides, including Sanders, are describing the influx of migrants trying to cross the southern border — including an uptick in those arriving with children — as a national security crisis. And like senior administration officials on the Thursday night teleconference, she repeatedly tried to press the Mexican government to do more within its own borders.

“We want to work with Mexico. … We’ve been giving them advanced warning for months. We’ve asked them repeatedly and told them they have to do more,” Sanders told reporters after the cable news appearance. She said Mexican officials have on average three weeks to detect and detain migrants moving from their own southern border to that of the United States. (She did not provide supporting data.)

Grassley warned that “following through on this threat would seriously jeopardize passage of USMCA, a central campaign pledge of President Trump’s and what could be a big victory for the country.”

That signals a possible 2020 election-cycle showdown that could amount to a GOP civil war as the party tries to hold the White House and Senate, and faces an uphill fight in taking back the House.

“I support nearly every one of President Trump’s immigration policies, but this is not one of them,” Grassley said. “Following through on this threat would seriously jeopardize passage of USMCA, a central campaign pledge of President Trump’s and what could be a big victory for the country.”