WASHINGTON — The conservative Koch political network said on Monday that it would begin a multimillion-dollar advertising campaign to promote free trade, sharpening a disagreement with President Trump over tariffs and highlighting a growing rift between conservative donors and the Republican base on trade issues.
The paid media campaign from three Koch-affiliated groups — Freedom Partners, Americans for Prosperity and the Libre Initiative — will promote the traditional free-market view of open trade as beneficial to all countries involved. The groups said the advertisements would draw on a set of trade principles in line with that philosophy, including calling on Mr. Trump to scrap tariffs that he has threatened and already put in place.
The campaign comes at a moment of tension within the Republican Party, which has traditionally embraced free-market views but is now being led by a protectionist president who routinely threatens and imposes trade barriers that have long been anathema to many Republicans.
The billionaire Koch brothers, Charles and David, have long supported Republican candidates and causes, including Mr. Trump’s $ 1.5 trillion tax cut. But the Kochs have increasingly found themselves at odds with the president, and sometimes with Republican leaders in Congress, on other issues including trade and immigration.
They previously funded an ad campaign urging Congress and the president to assist millions of undocumented immigrants who were brought to the United States as children, and last week they bought web ads to support a Democrat, Senator Heidi Heitkamp of North Dakota, even tough she is a top Republican target in the midterm elections.
“The Trump administration has taken some incredibly positive steps for the American economy, but tariffs will undercut that progress and needlessly hamstring our full economic potential,” Tim Phillips, the president of Americans for Prosperity, said in announcing the advertising campaign.
James Davis, the executive vice president of Freedom Partners, said the campaign was “a demonstration of our long-term commitment to advance common-sense trade policies that will ensure America’s brightest days are ahead, and to directly confront the protectionist ideas that would hold us back.”
Along with pressing the administration to drop its tariffs on steel and aluminum imports and on Chinese goods, the group is calling on Mr. Trump to work on “modernizing” the North American Free Trade Agreement with Mexico and Canada and to re-engage in negotiations toward joining the Trans-Pacific Partnership alongside 11 Pacific Rim nations.
It is unclear how much of an impact the campaign may have on the Republican base. Mr. Trump’s embrace of protectionist policies, such as tariffs, has helped galvanize a rapid shift in attitudes among rank-and-file Republicans on trade. The Pew Research Center reported in May that Republicans are now equally likely to say free-trade agreements have been generally good or generally bad for the United States; in 2015, before Mr. Trump began a presidential bid that criticized trade deals heavily, Republicans were much more likely to say such agreements had been good for the country.
A survey conducted in early May for The New York Times by the online polling firm SurveyMonkey found that 78 percent of Republicans approved of Mr. Trump’s tariffs on steel and aluminum. A majority of independents and Democrats disapproved of the tariffs.
Mr. Trump’s tariff impositions and threats have drawn condemnation from top Republicans in Congress, but little legislative pushback. After Mr. Trump said last week that he would follow through on steel and aluminum tariffs against Mexico, Canada and the European Union, Speaker Paul D. Ryan of Wisconsin said he disagreed with the decision.
“There are better ways to help American workers and consumers,” Mr. Ryan said. “I intend to keep working with the president on those better options.”
Senator Mitch McConnell of Kentucky, the majority leader, said on Friday in Louisville that “I don’t think anything good will come out of a trade war, and I hope we pull back from the brink here.” But he said Republicans in Congress could do little to stop Mr. Trump’s actions.
“Under the trade law, the president has pretty much all the ability to do these things, so there’s not much we can do to impact it,” Mr. McConnell said. “It’s really an executive branch activity, and he’s got the authority to do what he’s chosen to do. It’s just that I think many of us feel that it shouldn’t be done.”
Republican leaders could try to counter Mr. Trump by working with Democrats to curb Mr. Trump’s trade powers. Senator Mike Lee of Utah has proposed such a bill, which Senator Patrick J. Toomey of Pennsylvania recently endorsed.
But Republican leaders appear to have little appetite for sweeping legislation. Instead, they seem content to advance more targeted measures, such as blocking the administration from softening its punishment of the Chinese telecommunications firm ZTE.
The rhetoric-heavy opposition from congressional Republicans to Mr. Trump’s trade agenda has drawn criticism from some other Republicans who frequently clash with Mr. Trump.
“My party, the Republican Party, has been in favor of free trade as long as I can remember,” Gov. John R. Kasich of Ohio, who finished well behind Mr. Trump in the 2016 Republican presidential campaign, said on Sunday on CBS’s “Face the Nation.”
But Mr. Kasich said he was “shocked at the fact that our leaders think they have got to — they have to ask permission from the president to do anything.” He called on Mr. McConnell and Mr. Ryan to stand up to Mr. Trump on the issue.
“I think they ought to make it very clear that they’re not going to just sit back and tolerate this,” he said, “that they’re going to do whatever they can do legislatively to send a clear signal.”