WASHINGTON - President Donald Trump and House Republicans stepped up their efforts to win congressional approval for the U.S.-Mexico-Canada trade accord on Tuesday, selling the plan as offering big benefits for American workers. But prospects remain uncertain as Democrats are in no hurry to secure a political victory for the president.

GOP lawmakers emerged from a meeting with Trump and urged quick action on the trade agreement. Supporters in Congress and business groups say they have a narrow window to push it through, given that lawmakers tend to avoid tough trade votes during election season.

There are a lot of big wins for American workers in this agreement, said House Minority Whip Steve Scalise, R-La. We'd like to see it move through Congress as fast as possible and create even more jobs with this growing economy.

Rep. Earl Blumenauer, D-Ore., the chairman of the House subcommittee that has jurisdiction over trade, said the pact needs adjustments to be worthy of support.

Some Republican lawmakers also have concerns. Sen. Chuck Grassley of Iowa, the Republican chairman of the Senate Finance Committee, maintains that the president should lift steel and aluminum tariffs on products brought in from Canada and Mexico as a first step to getting the trade agreement through Congress.

Trump's top trade negotiator, Robert Lighthizer, told lawmakers during a recent congressional hearing that if they don't pass the trade agreement, the United States will have no credibility at all with future trading partners, including China.

There is no trade program in the United States if we don't pass USMCA. There just isn't one, Lighthizer said.

The White House's legislative affairs team has talked to more than 290 members of Congress and staff over the past two months to push the deal. But the administration knows that making changes in the agreement to win over lawmakers could jeopardize support for the pact from Canada and Mexico.

Sen. Joni Ernst, R-Iowa, told reporters recently that many in her state's agricultural community are still with the president, but if we don't get the trade deals done, they could turn quickly.

She said, We need to start wrapping this baby up.

The trade deal is designed to supplant the North American Free Trade Agreement , which took effect in 1994 and gradually eliminated tariffs on goods produced and traded within North America.

U.S. trade with its NAFTA partners has more than tripled since the agreement took effect, and more rapidly than trade with the rest of the world.

But Trump has called NAFTA a disaster for the United States. The new pact his administration negotiated is meant to increase manufacturing in the United States. Trump is warning that if lawmakers don't approve the pact, the U.S. may revert to what he has described as pre-NAFTA.

Blumenauer is looking to make changes to the agreement in four areas: enhancing environmental and labor protections, ensuring enforcement of the agreement, and taking on protections for pharmaceutical companies that he believes drive up drug costs for consumers.

I don't think anyone wants to blow it up, but there is interest in strengthening it, Blumenauer said.

Rep. Vern Buchanan of Florida, the ranking Republican on the trade subcommittee, said he believes the vast majority of Republicans will end up voting for the agreement. He's tried to assure Democratic colleagues that Republicans were open-minded to try and get some things done to address their concerns.

Still, Republicans conceded that Democrats are in charge of the calendar.

Ambassador Lighthizer has said legislation will be sent to the Hill when Speaker Pelosi gives the green light, said Rep. Kevin Brady, the ranking Republican on the House Ways and Means Committee. Those of us here today are continuing to work with Democrats to address any enforcement issues or any fine-tuning they'd like to see on this agreement, but we think it's crucial ... that we come together and pass this new agreement and get it to the president's desk this summer.

Canadian officials have been lobbying the U.S. to end Trump's steel and aluminum tariffs and have suggested that approval by Canada's Parliament could be conditioned upon them being lifted. David MacNaughton, Ottawa's ambassador to Washington, has said it will be a tough sell to pass if the tariffs are still in place.

Dan Ujczo, a trade lawyer and Canada-U.S. specialist in Columbus, Ohio, said the trade deal could pass relatively quickly once the tariffs are removed.

But Scalise described the tariffs as helping to create more leverage to get a deal done.

In Mexico, the administration of then-President Enrique Pena Nieto spearheaded Mexico's negotiations, but representatives of current President Andres Manuel Lopez Obrador were deeply involved in the talks to ensure an agreement that both the outgoing and incoming administrations could live with.

Allies of Lopez Obrador, who took office Dec. 1, enjoy a large majority in the Mexican Senate, so passage of the agreement would seemingly go smoothly.

Kenneth Smith Ramos, who was chief negotiator for Pena Nieto's government and now works as an international trade consultant at Mexico City-based AGON, said Mexican enthusiasm for the deal could dim though if there are significant new demands on labor, pharmaceuticals, the environment or other issues.

We made some important concessions, he said, adding that if the U.S. still wants more, then that starts to unbalance the agreement and there may be a growing opposition in Mexico.