Prominent senators looking to restrict President Trump’s ability to enact tariffs are divided over which bipartisan legislation to support.

Sens. Pat Toomey, R-Pa., and Mark Warner, D-Va., introduced legislation in January that would limit Trump's ability to unilaterally implement tariffs on national security grounds by requiring congressional approval first. Business lobbies such as the Chamber of Commerce, which oppose tariffs, have endorsed the Toomey-Warner approach.

Legislation introduced a week later by Sens. Rob Portman, R-Ohio, and Doug Jones, D-Ala., dubbed the Trade Security Act, would also curb Trump's ability to levy tariffs, but would require approval from the Defense Department, not Congress, which would only have to be consulted. The bill would also give Congress the ability to stop the tariffs via a simple resolution of disapproval.

The dueling bills reflect a broader ambivalence within Congress over Trump’s tariff power, says Rep. Kevin Brady, R-Texas, the ranking Republican on the Ways and Means Committee. Many lawmakers want more control over the process, but they also support the way Trump has used his tariff powers so far.

“There is a growing sense that Congress should retain more of the tariff-increasing powers that have been ceded to the White House over the last 50 years,” Brady said. “But there is also a very strong sense that the president is exactly right to challenge China on trade.”

Both the Toomey-Warner and Portman-Jones bills would rewrite the administration's ability to enact tariffs under Section 232 of the 1962 Trade Expansion Act. That section allows tariffs to be enacted without congressional approval provided that they protect national security. Trump has used the authority to enact blanket tariffs of 25 percent on steel and 10 percent on aluminum on the grounds that protecting domestic industries ensures that the U.S. military has the metals it needs for tanks, planes, and other materiel.

While domestic steelmakers such as Nucor are expanding production thanks to the tariffs, manufacturers that use steel, such as Ford and Caterpillar, are facing steeper costs for raw materials. Manufacturers have lobbied to remove the tariffs.

The Toomey-Warner bill has eight cosponsors, about equally split between both parties, while the Portman-Jones bill has six, equally split. Only one senator, Tennessee Republican Lamar Alexander, is supporting both. Both bills have bipartisan companion versions in the House.

Congressional aides say the similar nature of the bills has sown confusion on Capitol Hill over whose version does what, complicating the effort to limit Trump's powers.

Portman, a former U.S. trade representative during the Bush administration, argues that his more “balanced approach” has a better chance of passage. “The goal of his legislation is to stop the misuse of this 232 statute but preserve this tool for genuine national security threats in the future,” said Portman spokeswoman Emily Benavides.

Toomey responds that the rival Portman-Jones bill “does nothing whatsoever to restore any role to Congress.” Giving Congress the power to rescind tariffs with a resolution of disapproval is meaningless, he says. “Under current law, on any day of the week Congress could pass a law that rescinds those tariffs.”

Trump could veto any legislation that attempts to tie his hands. Asked about the possibility, Toomey replied, "We're not looking that far ahead." Even the less aggressive Portman-Jones bill risks a presidential veto. The best chance for either bill would be to combine it with some must-pass legislation to get it past Trump. A White House spokesman did not respond to a request for comment.

Rep. Ron Kind, D-Wis., is co-sponsoring the House versions of both bills, but believes that Portman’s less far-reaching Trade Security Act is the one to bet on. “I expect [that] bill will have greater success,” Kind’s spokesman Aaron White said.

Senate Finance Committee Chairman Chuck Grassley, R-Iowa, has called Toomey’s bill "too blunt" but nevertheless hedged his bets. "I haven’t endorsed any approach, but we’re going to do something on 232," he told reporters in early February. "We’re going to have to sit down and see what kind of compromise, hopefully bipartisan, that we can agree to."