Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellFEC flags McConnell campaign over suspected accounting errors Poll: 59 percent think president elected in November should name next Supreme Court justice Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' MORE (R-Ky.) on Thursday crushed any hope that Congress could pass a sweeping Pacific Rim trade agreement before the 2016 elections.

McConnell, who has expressed concerns about the 12-nation Trans-Pacific Partnership (TPP) and has yet to take a stance, said President Obama is risking defeat of his signature trade deal if he tries to push for passage before a lame-duck session next year.

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“It certainly shouldn’t come before the election," McConnell told The Washington Post in an interview.

"I think the president would be making a big mistake to try to have that voted on during the election. There’s significant pushback all over the place," he said.

Obama is already facing a slim margin of support in each chamber.

With minimal support from his own party, Republicans who granted Obama fast-track authority on trade deals have said support didn't mean automatic passage for the TPP pact.

“I think it would be a big mistake to send it up before the election,” McConnell said.

He also raised the specter that the deal may not get done before Obama leaves office, noting that the next president will have the same fast-track authority granted to Obama this summer.

"The next president, whoever that is, will have the authority to either revisit this one, if it doesn’t pass, or finish the European deal or other deals, and give Congress a chance to weigh in on it,” McConnell said.

While McConnell has expressed support in the past for trade, he has warned the White House not to target tobacco growers in a final deal.

The deal includes a provision that gives countries more power to regulate manufactured tobacco products, such as cigarettes, as part of any efforts to protect public health. Under the exemption, companies can’t challenge tobacco control measures under the Investor-State Dispute Settlement process.

The White House has argued that the tobacco provisions are narrowly focused on health issues and don't affect the trade of tobacco leaf.

But the move has already led to the loss of Republican votes on both sides of the Capitol.

The timeline for when Congress might receive the agreement is fluid.

Many supportive House Democrats have said there is a small window within the first three months of the year where they would feel comfortable voting for the TPP.

But if it can't be done quickly, then lawmakers such as Rep. Gerry Connolly (D-Va.) have said there would be no harm in waiting until the pressure of the elections is off in the lame-duck session.

And McConnell isn't the only Senate Republican throwing a wrench into the works.

Senate Finance Committee Chairman Orrin Hatch (R-Utah), who helped craft the fast-track legislation, has raised major concerns about the deal, especially for the TPP's protections for high-tech medicines called biologics. Pharmaceutical companies pushed for the U.S. standard of 12 years of data protections but got eight.

Hatch said he has met with U.S. Trade Representative Michael Froman and told him that he is willing to work with the White House but that some changes have to be made.

Hatch said Froman seemed open to working on several issues.