After a visit to the White House and Capitol Hill on Thursday, Canadian Prime Minister Justin Trudeau said he is optimistic about the prospects of the United States-Mexico-Canada trade agreement, but added he hoped obstacles in the U.S. don’t lead to reopening negotiations.

Trudeau, speaking at a news conference at the Canadian embassy, lauded the “very strong and positive relationship with the United States” that he said came out of USMCA negotiations that were “contentious at times.” 

He cited concerns about the possible reopening of negotiations as Congress works on the agreement.

“Any reopening of NAFTA could lead to not just lengthy further negotiations that we all were quite pleased were behind us, but also may lead to worse outcomes for Canadians and for Canada,” the prime minister said, using the acronym for the North American Free Trade Agreement. The USMCA is the replacement for NAFTA.

“We can’t overstate how important free trade is to the Canada-U.S. relationship,” he said. “Millions of people and businesses depend on a strong economic partnership between our two countries to make ends meet. That’s why we worked incredibly hard with our North American partners to secure a new NAFTA.”

Trudeau was in Washington the day after the Mexican Senate ratified the agreement 114-0.

President Donald Trump said Thursday that Canada is doing “very well” at approving the new agreement, an assertion Trudeau endorsed.

The Canadian House of Commons, which adjourned Thursday until Sept. 16 with the implementing legislation still in committee, could return before then for a ratification vote. The House’s website shows a notice saying the date of return is subject to change without notice.

The pact’s prospects in the U.S. are less clear. There is no timetable in place for the House to take up legislation to approve the deal, and the final text of the agreement is not yet settled.

Speaking in the West Wing alongside Trudeau on Thursday, Trump was cautious about the prospects. But he said he thought Speaker Nancy Pelosi would advance the deal.

House Democrats are seen as the major potential obstacle. Pelosi has criticized the agreement in its current form. Democrats are most concerned about enforcement of labor and environmental provisions, and by a 10-year pricing monopoly on biologics.

“We all agree that we must replace NAFTA, but without real enforcement mechanisms we would be locking American workers into another bad deal,” Pelosi said in a statement last month. “A new trade agreement without enforcement is not progress for the American worker, just a press release for the president.”

Nonetheless, before her meeting with Trudeau, the California Democrat said she was “optimistic and hopeful” about the future of the USMCA.

“We want to get on a path to yes,” she said.