Farm Republicans revolt against Trump’s steel “tax.” Warn it’ll cost him at the polls. | McClatchy Washington Bureau

Another White House surprise, another Republican revolt.

GOP lawmakers from farming states sharply warned President Donald Trump Thursday that his decision to impose tariffs on steel and aluminum imports will cost Americans consumers — and could be devastating for him at the polls.

Kansas Sen. Pat Roberts, the Republican chairman of the Senate Agriculture Committee, struggled to find words to describe his emotions after being blindsided by Thursday’s news that Trump would impose tariffs of 25 percent on steel and 10 percent on aluminum imports that sent stocks spiraling amid fears of a trade war.

“These are the people who voted for the president,” Roberts said. “These are his people. One county in Kansas even voted for him 90 percent and they’re not going to be happy at all about this.”

Roberts was joined in criticizing the proposal by U.S. Senator Ben Sasse, a Republican from neighboring Nebraska. Together they said the impact on farm states would be costly if foreign governments retaliate with tariffs on imports of U.S. goods, such as agricultural products.

“Let’s be clear: The President is proposing a massive tax increase on American families. Protectionism is weak, not strong. You'd expect a policy this bad from a leftist administration, not a supposedly Republican one,” Sasse said.

The stern admonishing was reminiscent of the pushback Republicans and conservatives gave Trump on immigration following a meeting in January.

However, Trump said the tariffs would help right decades of unfair trade policies. Trump told the group of executives who gathered at the White House, including representatives from Nucor Corp., AK Steel Holding Corp. and U.S. Steel Corp., that “you will have protection for the first time in a long while.”

Trump said the full plan will be announced next week. The White House would not provide any specific details, including whether some trade partners would be exempt.

But Roberts and other Republicans from the Senate Finance Committee described the penalties as a ultimately “consumer tax,” that would boomerang badly on the very rural and middle-class voters who supported his election in 2016.

Roberts worried that imposing the steep tariff could also wipe out any benefits from tax reform if higher manufacturing costs are passed on to consumers. He fears that unilateral withdrawal from NAFTA could be next on Trump’s chopping block.

“Let’s certainly hope not,” he said.

Trump also took criticism from other GOP corners on Capitol Hill.

Rep. Mark Meadows, R-N.C., chairman of the Freedom Caucus and a Trump supporter, tweeted that "manufacturing will ultimately be the loser with these protectionist policies."

Democratic Sen. Claire McCaskill, who represents a state Trump won by nearly 20 percent of the vote, said she is also concerned that Trump is starting a trade war that will punish Missouri’s manufacturing and agriculture sectors.

“What’s being proposed here will fall squarely on the shoulders of the thousands of the Missourians in manufacturing jobs, and on the thousands more farmers who may see swift retaliation by foreign countries against their goods.” McCaskill said.

While steel company stocks rose on the announcement, the Dow Jones industrial average showed less bullishness, dropping 420.22 points, or 1.68 percent, on concerns protectionist trade policies could ripple across U.S. corporations and consumers.

The Business Roundtable said the tariffs would backfire and “could embolden other countries to impose ‘national security’ tariffs on U.S. exporters.” Americans for Prosperity, a nonprofit funded by Kansas billionaires Charles and David Koch, blasted the idea as perpetuating “a harmful practice in which the government is able to hand-pick winners and losers in specific industries.”

Both Mexico and Canada have raised concerns about such tariffs as part of NAFTA negotiations. On Thursday, Canada threatened retaliation if it was subject to any restrictions.

“It is entirely inappropriate to view any trade with Canada as a national security threat to the United States. We will always stand up for Canadian workers and Canadian businesses,” said Chrystia Freeland, Canada's Minister of Foreign Affairs. “Should restrictions be imposed on Canadian steel and aluminum products, Canada will take responsive measures to defend its trade interests and workers.”

Some Democrats praised the deal.

Ohio Sen. Sherrod Brown, one of 10 Senate Democrats up for reelection in states that Trump won in 2016, hailed the measure and said he has repeatedly urged Trump and Commerce Secretary Wilbur Ross to provide the steel industry with some relief. He met with Trump at the White House last month to encourage him to take the move.

He said he welcomed action which is “long overdue for shuttered steel plants across Ohio and steelworkers who live in fear that their jobs will be the next victims of Chinese cheating.”

And Sen. Bob Casey, D-Penn, who is also up for reelection in another state Trump won, similarly hailed the move as long overdue.

“It has taken the administration far too long, but today’s announcement of an intention to act next week is a welcome step," he said.

Emma Dumain, Lesley Clark, Brian Murphy and Anita Kumar contributed.