WASHINGTON -- A bipartisan group of 10 senators introduced longshot legislation Wednesday to require Congress to sign off on tariffs imposed in the name of national security, defying President Donald Trump on a bedrock issue that once defined the GOP.

Congressional Republicans are mostly at odds with what they view as Trump's protectionist instincts on trade. Despite much hand-wringing, prospects for any bill to challenge him remain uncertain. Many Republicans are hesitant to confront Trump in a legislative showdown that could end badly for them. Doing so could court a veto and bruise their standing with Trump voters they need in midterm elections.

Senate Majority Leader Mitch McConnell, R-Ky., indicated he was not interested in spending too much time on the effort presented behind closed doors Tuesday by its chief proponent, Sen. Bob Corker, R-Tenn., saying he preferred to focus on "getting bills passed." And the second-ranking Republican, Sen. John Cornyn of Texas, said he hoped Republicans concerned about the tariffs could prevail on the president to reverse course. He visited the White House Wednesday for talks.

"Not everything we do has to be legislative. Part of this job is persuasion," said Cornyn. He said lawmakers would "continue to make the case" with the president and his staff, which he noted is divided.

Trump took office promising to rip up trade deals and crack down on unfair trading practices. But that campaign slogan is at odds with Republicans' longstanding preference for free markets and open trade. The standoff is raising an uncomfortable question: If Republicans can't confront Trump on trade, can they challenge him on anything?

"For Republicans, this is who we are," said Sen. Jeff Flake, R-Ariz. "If we believe our own rhetoric -- on trade, tariffs and congressional prerogative -- I hope it does come to a vote."

The idea being pursued by Corker, Sen. Pat Toomey, R-Pa., and others who have been meeting privately -- and with Democrats -- would be narrowly crafted legislation requiring congressional approval of the tariffs Trump has imposed in the name of national security.

They're targeting Trump's reliance on the so-called 232 authority, named from Section 232 of the Trade Expansion Act of 1962, which allowed the administration to impose tariffs of 25 percent on imported steel and 10 percent on imported aluminum from Mexico, Canada and the European Union, some of the U.S.'s top allies. The senators are also hoping to halt Trump's threat to slap tariffs on auto imports, including those from Japan.

"I fail to see the national security threat when a Pennsylvanian decides to buy a Toyota Corolla," Toomey said.