Despite a push from some Senate Republicans to intervene on president's trade talks, Grassley thinks that approach would undermine ongoing negotiations.

Despite U.S. Sen. Charles Grassley's concerns about how President Donald Trump's trade tactics are affecting Iowa agriculture, he doesn't think Congress should intervene to restrict his negotiations — not yet, at least.

Iowa's senior Republican senator told reporters Wednesday legislative interference in the midst of the president's negotiations would send a "bad signal" to America's trading partners.

His comments come at a time some GOP senators want to push legislation limiting a president's power to unilaterally levy tariffs against other countries. Senators were expected to vote Wednesday on the bill, led by Sen. Bob Corker of Tennessee.

Grassley, who described himself as a "free-trader," said there "probably" needs to be restrictions put on a president's ability to tax goods imported from other countries.

"But not in the middle of negotiations," he said.

Grassley and his fellow Iowa senator Joni Ernst have been vocal about their concerns over how Trump's no-holds-barred approach to trade negotiations with countries like Mexico, Canada and China will affect the state's farm economy, and how they already have.

This week, the president said he was ready to impose tariffs on an additional $200 billion worth of Chinese products.

Grassley, who visits all of Iowa's 99 counties every year, said constituents always bring up concerns at town hall meetings about the effects of Trump's trade tactics.

"I never really had people tell me the president shouldn't be negotiating as he is ... which tells me they want the president to succeed," he said. "But they also know if the president doesn't get a better deal for the United States and his brinkmanship takes us over the brink, it's going to be catastrophic."

The Washington Post has reported on a March poll, from the trade site Agri-Pulse, that showed out of 750 Plains states and Midwestern farmers, 67 percent voted for Trump in 2016 and 45 percent said they would do so again.

While at a NATO summit Wednesday in Brussels, Trump took to Twitter to reassure farmers he was "fighting for a level playing field."

"I am in Brussels, but always thinking about our farmers. Soy beans fell 50% from 2012 to my election. Farmers have done poorly for 15 years. Other countries' trade barriers and tariffs have been destroying their businesses. I will open things up, better than ever before, but it can't go too quickly. I am fighting for a level playing field for our farmers, and will win!"

On Sunday, Ernst appeared on CBS' Sunday program "Face the Nation," discussing how combative trade policies have put Iowa and other agricultural states "in the cross-hairs."

She said Republican voters, including many farmers, "think that he is doing the right thing," but "farmers and ranchers are always the first to be retaliated against in these types of trade negotiations, and the tariffs that have been imposed and the retaliation stemming from that puts us in a very vulnerable position as our markets go down."

Ernst said she has encouraged the president to clear-up his ongoing trade disputes quickly, preferably "sooner rather than later."