WASHINGTON — President Donald Trump’s promise to quickly pass a revamped North American Free Trade Agreement has been upended by the midterm elections, with Democrats who will soon control the House vowing to withhold their support to extract greater protections for American workers.

Administration officials remain confident they will corral the votes for the new United States-Mexico-Canada Agreement, which Trump negotiated in September to claim a big win on one of his signature issues before the November elections.

While White House officials considered pushing the revised deal through the coming lame-duck session, they did not want to risk a backlash from lawmakers in both parties.

Democrats, emboldened by their midterm win and eager to outshine Trump as defenders of the American worker, are unlikely to sign off on any deal that does not include significant changes that labor leaders and newly elected progressives are demanding. That could involve reopening negotiations with Mexico, although U.S. and Mexican negotiators have publicly ruled out that possibility.

“Trump made it seem like this was a done deal, but there is a long, long way to go,” said Rep. Bill Pascrell, D-N.J., who is likely to be named chairman of the House Ways and Means Subcommittee on Trade.

The House will consider the agreement first under the Constitution’s provision mandating that revenue bills originate in the lower chamber.

A vote could take up to nine months or longer, according to senior administration officials.

Democrats and their allies in manufacturing unions maintain that the new requirements, while an improvement on the original NAFTA, do not go far enough.