WASHINGTON -- President Donald Trump welcomed Canadian Prime Minister Justin Trudeau to the White House as the two leaders work to get a replacement for the North American Free Trade Agreement over the finish line.

At Trump's insistence, the U.S., Canada and Mexico agreed to an update of the 25-year-old agreement. Trump told reporters Thursday before meeting with Trudeau that "we've come a long way" on a replacement.

Trump predicted the deal would gain bipartisan support and asserted that it would pass easily if a vote were held the day after next year's presidential election.

Mexico this week became the first of the three nations to ratify the agreement.

The White House recently moved to ease passage of the agreement by lifting tariffs on imported steel and aluminum from Canada and Mexico. It also took steps that would allow the administration to submit legislation necessary to implement the trade deal in time for lawmakers to vote before the August recess, if they so choose.

In the end, it comes down to whether House Speaker Nancy Pelosi, D-Calif., will bring the bill to a vote. She insists that changes are needed to generate Democratic support, and has appointed a working group to meet with United States Trade Representative Robert Lighthizer on changes that would ease Democratic lawmakers' concerns.

"My hope is that over the course of the next couple of weeks we can make substantial progress," Lighthizer told a Senate panel Tuesday.

Labour unions, a key Democratic constituency, are seeking assurances that Mexico will enforce enhanced labour standards for workers there because that would reduce the incentive for U.S. companies to move their plants and jobs south of the border. The new deal requires Mexico to encourage independent unions that will bargain for higher wages and better working conditions.

"If the president insists on a premature vote, we'll have no choice but to oppose it," AFL-CIO President Richard Trumka said this week at a union event in Pittsburgh.