Perhaps no issue highlights how President Trump has remade the Republican Party better than trade.

In the past, Republican politicians staunchly championed free trade, or opening up America’s borders to other countries’ products and services. Now, a Republican president is putting billions of dollars in tariffs on Chinese products as a way to close the U.S. to trade practices he deems unfair. And congressional Republicans aren’t even trying to stop him.

Republican senators say they aren’t happy with the tariffs, both on principle and because it puts American farmers in their states in financial jeopardy. But as Politico’s Burgess Everett and Marianne Levine smartly detail, Republican senators aren’t planning to do much about it.

“The retaliatory tariffs will have a significant consequence to Kansans,” Sen. Jerry Moran (R-Kan.) told Politico. But he went on to say there’s not much the Senate can do about it. “Really this authority rests in the president.”

It wasn’t always this way. A year ago, when Trump first started putting tariffs on other country’s products, Republicans seemed more willing to put up a fight. They said what the president is doing amounted to a tax increase on the American people. (The logic is that companies that have to pay tariffs for importing aluminum and steel and an increasing number of Chinese products will pass that higher cost onto consumers.)

Then-Senate Finance Committee Chairman Orrin G. Hatch (R-Utah), one of Trump’s most steadfast allies during the tax debate, said this in March 2018: “Tariffs on steel and aluminum are a tax hike the American people don’t need and can’t afford.”

And Sen. Ben Sasse (R-Neb.) simply called tariffs bad policy: “Let’s be clear: The president is proposing a massive tax increase on American families."

Republicans tried to lobby Trump behind the scenes to drop the tariffs. They considered a bill to limit them.

This time around, Republican senators are still expressing their frustration with Trump, but there’s a marked shift in language, almost a resignation that they’ve lost this battle.

Sen. Charles E. Grassley (R-Iowa), the current Senate Finance chairman, represents a state on the front lines of the economic pain created by tariffs. He is leading a bipartisan effort to introduce legislation that would allow Congress to weigh in on any tariffs the president issues for national security reasons. He has also said he’ll block Trump’s renegotiated North American trade deal as long as Canadians and Mexican steel and aluminum is tariffed, Politico reports. Grassley has written op-eds opposing Trump’s tariffs and told The Post’s Damian Paletta he plans to write a letter to Trump about the recent tariffs because all other negotiations have failed. “I’m not sure if you talk to him face to face he hears everything you say,” Grassley said.

The Republican-controlled Senate could pass legislation led by Grassley taking back some of its authority to approve or deny tariffs. (Right now the White House can basically unilaterally impose tariffs.) It would probably be vetoed by the president if it passed, but it would demonstrate that Republicans are willing to challenge their own president.

They could vote on a resolution of disapproval, as they did for Trump’s national emergency declaration at the border. It’s symbolic, but at least it would register for the history books that the Republican Party under Trump is not entirely a pro-tariff party.

But Republicans right now have no plans to do any of that.

One reason is timing. They are a year and a half out from elections where the base is their party has largely aligned with Trump on trade. Stand up to Trump on trade, risk getting a primary challenger, is the logic.

But that doesn’t explain why the Republican Party has shifted so much on trade under its congressional leaders’ feet. To some extent, that requires a deeper analysis than the present moment can provide. The reasons likely align with Trump’s rise: Americans’ growing sense of economic inequality, the feeling that globalization has left them behind, and Trump’s simplistic prescriptions that closing America’s borders — from China and Latin immigrants — can staunch the tide.

During the 2016 campaign, Republican voters’ opinions of free trade seemed inversely proportional to then-candidate Trump’s rise. Toward the end of the campaign, Republican voters’ opinions of free trade were at their lowest since 2009.

A June 2016 survey by the Public Religion Research Institute and the Brookings Institution found that a majority of Americans said free-trade agreements were more harmful than helpful — with Trump supporters the group most inclined to say they are harmful.

There are some murmurs that farmers who have stood by Trump in states he won in 2016 are starting to break. Soybean farmers, pork producers and cherry producers in particular have said they’re struggling with the tariffs already in place, Paletta reports.

Sen. Roy Blunt (R-Mo.) warned as much to Politico: “They can feel it. The farm community up ‘til now has really supported the president without flinching. But eventually you flinch."

But for now, Republican lawmakers are stuck inside a party that, when it comes to a consequential economic issue directly affecting many of their constituents, they don’t recognize. It’s just one of many ways the Republican Party has been remade to the party of Trump.

This post has been updated to include legislation Sen. Grassley is working on to have Congress take back some power in the tariff process.