WASHINGTON — House Democrats return to Washington on Monday facing a difficult choice: Should they hand President Trump a victory in the midst of a heated impeachment battle or walk away from one of the most progressive trade pacts ever negotiated by either party?

The Trump administration agreed with Canada and Mexico on revisions to the North American Free Trade Agreement one year ago, but the deal still needs the approval of Congress. A handshake agreement with the administration in the coming days would give the Democratic caucus a tangible accomplishment on an issue that has animated its base. It could also give Democrats a chance to lock in long-sought policy changes to a trade pact they criticize as prioritizing corporations over workers, laying the groundwork for future trade agreements.

Those factors have coaxed Democrats to the table at an improbable moment, when Washington is split by partisan fights and deeply divided over an impeachment inquiry. After months of talks, including through the Thanksgiving break, both sides say they’re in the final phase of negotiations. But Democrats insist the administration must make more changes to the labor, environmental and other provisions before Speaker Nancy Pelosi of California will bring legislation implementing the new United States-Mexico-Canada Agreement to a vote.

“By any standard, what we’ve already negotiated is substantially better than NAFTA,” said Representative Richard E. Neal of Massachusetts, who is heading the Democratic group negotiating with the administration. “Labor enforcement, in my judgment, is the last hurdle.”