Several Republican lawmakers did Tuesday what few of their colleagues have since Donald Trump took office: They challenged one of the president’s core principles to his face.

Sen. Roy Blunt was among those who warned Trump against starting a trade war with other countries on which many U.S. companies buy goods and materials.

“We need to be careful here that we don’t start a reciprocal battle on tariffs,” the Missouri Republican said, telling the former New York real estate executive that companies in his state buy materials from other countries. Blunt used “reciprocal,” a favorite description of the president when speaking of how he wants to overhaul U.S. trade tactics. 

[‘Crisis Budgeting’ Likely Ahead Despite White House Claim]

“We make aluminum and we make steel in Missouri,” Blunt said, “but we buy a lot of aluminum and we buy a lot of steel as well.”

Blunt and other Republicans’ pressing of Trump came as the president declared of American officials: “We’re like the stupid people [on trade].”

Other members of the bipartisan group meeting with Trump in the Roosevelt Room issued similar warnings to the president, but he showed no signs of giving ground on his intention to slap tariffs on countries his administration deems guilty of “unfair” trade practices.

Sen. Todd Young, R-Ind., urged the president to take a “balanced approach.” Young also told Trump he should make China his administration’s “main target” on trade. Trump replied: “We’ve spoken to them very strongly.”

GOP Sen. Patrick J. Toomey, R-Pa., urged Trump to proceed with his trade plans “very, very cautiously.” Toomey also warned the “America first” president that slapping tariffs on other countries and similar moves could “invite retaliation.” But Trump responded by saying U.S.-made motorcycle manufacturers face 50 percent to 75 percent taxes on their bikes in India.

“I say we should have reciprocal taxes,” said Trump, labeling India’s tactics “very unfair.”

[The Curious Case of Melanija Knavs]

Trump told the lawmakers and reporters that U.S. aluminum and steel imports are being “decimated” by “dumping.”

Other countries “are dumping and destroying our industries,” Trumps said. “We can’t let that happen,” noting his administration remains in the midst of a study on imposing new tariffs — adding he may also order quotas on goods.

Trump spoke about the “empty factories, steel factories” he saw during the 2016 campaign.

“I’ve been looking at them for two years as I went around campaigning.,” the president said. “If we ever have a conflict we don’t want to be buying steel for a country we are fighting.”

Oregon Democrat Ron Wyden, the ranking member of the Senate Finance Committee, said Democrats urged the president in the meeting to quickly decide if tariffs or other steps to limit steel imports are necessary to protect national security.

Wyden said he told Trump it was hard to advise him since the Commerce Department has not given him its investigative report on steel despite requests.

Ellyn Ferguson contributed to this story.Correction Feb. 14 10 a.m. | An earlier version of this story misidentified Indiana Sen. Todd Young’s title.