House Democrats will control the fate of one of President Donald Trump's top priorities as they return to Washington this week.

The president has pushed for swift approval of his replacement for the North American Free Trade Agreement, a top economic and political priority ahead of the 2020 election. Democrats have shown little urgency in moving to ratify the new United States-Mexico-Canada Agreement as signed by the three countries last year.

The White House has contended House Speaker Nancy Pelosi could put the deal to a vote at any time and it would pass the Democratic-held House. But the speaker and top Democratic negotiators still have concerns about whether it goes far enough to protect American workers and the environment. They also worry that a piece of the agreement could raise drug prices for U.S. consumers.

Democrats expect the pace of their talks with the Office of the U.S. Trade Representative to pick up after they return to Washington. Some members — many of them freshmen who helped Democrats flip the House by winning swing districts — have pushed for a vote on the deal before the end of the year. Even so, Pelosi has not yet committed to firm timing on a vote.

"The substance will determine the timing," Pelosi spokesman Henry Connelly said when asked if a vote could happen in 2019.

The next few months could prove pivotal for Trump's trade agenda, one of the planks that helped to propel him to the White House. He has taken more heat as his trade war with China, the world's second-largest economy, escalates, and fears about slowing global growth spread. Farmers and other businesses damaged by the trade conflict want to see the USMCA approved to end the uncertainty about their access to key Canadian and Mexican markets.

Much hinges on American trading relationships with its neighbors, which expanded after NAFTA went into effect in 1994. The U.S. sent about $300 billion in goods to Canada last year, more than any other country. It exported about $265 billion in products to Mexico, its second-largest market.

Democrats and Republican Trump alike have lamented that NAFTA helped to sap American manufacturing jobs in favor of cheaper Mexican labor. During remarks pushing for USMCA's passage last month, the president called NAFTA "one of the world's worst trade deals ever" and a "disaster for the country."

The U.S., Canada and Mexico made a few key changes to NAFTA last year. USMCA puts stricter rules on the country of origin for auto parts and requires almost half of those products to be made by workers earning $16 an hour or more. It also expands American access to the Canadian dairy market and aims to modernize copyright and digital trade rules.

Of the three countries, only Mexico's legislature has ratified the deal.