Enrique Pena Nieto, Mexico's president, from front left, U.S. president Donald Trump, and Justin Trudeau, Canada's prime minister, sit for photographs as Ildefonso Guajardo Villarreal, Mexico's secretary of economy, from back left, Robert Lighthizer, U.S. trade representative, and Chrystia Freeland, Canada's minister of foreign affairs, stand after signing the United States-Mexico-Canada Agreement (USMCA) at the G-20 Leaders' Summit in Buenos Aires, Argentina, on Friday Nov. 30, 2018.

President Donald Trump's trade deal with Canada and Mexico faces a treacherous path to approval in a split Congress, so the administration is planning to lean heavily on grassroots lobbying to sell the plan to skeptical voters and lawmakers.

The campaign, called Trade Works for America, is in the early stages of a multimillion dollar marketing blitz including television ads, congressional outreach and messaging to employees in industries that could be affected. The effort was assembled by veteran Republican operative Phil Cox.

"Our job is really to go out and educate the public about the benefits of USMCA," Cox told CNBC, referring to the trade deal. "We have a great opportunity to sort of define what this agreement is and to really talk about the benefits."

It's been nearly four months since the U.S., Canada and Mexico signed the deal to replace the North American Free Trade Agreement. Trump must sell House Democrats on his signature trade deal — and persuade Senate Republicans to stomach labor-friendly provisions to win the left over.

Cox sees the opportunity as a blank slate. Most voters now have a negative association with NAFTA, thanks to Trump's frequent attacks on the deal, which went into effect during the early years of President Bill Clinton's administration. But polling shows Americans don't know much about the new agreement.

Source: Trade Works for America

That conclusion was drawn from surveys in four crucial states — California, New Mexico, Michigan and Virginia — specifically in swing districts that favored Trump in 2016 but elected a Democrat in the November 2018 midterms. After Trade Works for America tested its messaging about the benefits of the deal on those voters, support rose to 72 percent from 47 percent — with the biggest increase among Democrats, women and voters younger than 54.

Lawmakers representing those districts were noncommittal. Spokespersons for Reps. Abigail Spanberger, D-Va., and Xochitl Torres Small, D-N.M., said they were waiting to see the legislation.

Reps. Elissa Slotkin, D-Mich., and Josh Harder, D-Calif., were among the signatories to a March 12 letter to U.S. Trade Representative Robert Lighthizer, asking for input into the legislative process, concluding "we expect continuous and meaningful consultations with you and the Administration to shape President Trump's trade agenda this Congress."

Source: Trade Works for America

The text of the trade agreement is expected to be sent to Capitol Hill in April, starting a 90-day legislative clock and kicking the sales pitch on both sides of Pennsylvania Avenue into high gear. Around that time, a much-anticipated opinion on the economic impact will be released by the the International Trade Commission, which lawmakers say is a precursor for hearings. Democrats expect Mexico to pass new labor laws that are viewed as prerequisites for their party's support here in the U.S.

"We need that first of all," said Rep. Bill Pascrell, D-N.J., a member of the House Ways and Means panel's subcommittee on trade. "If they don't act, there's definitely no chance of getting the votes."

White House officials have been increasing their outreach on both sides of the aisle. Trump was slated to meet with a group of House Republicans at the White House on Tuesday to discuss their concerns with the deal. Lighthizer has met individually with the congressional whips or vote counters, the House Ways and Means Committee, the Hispanic Caucus and the Blue Dog Democrats. White House officials said he had a "good rapport" with House Democrats when he met with the whole group on March 13.

"None of us are saying no at this point," said Rep. Pramila Jayapal, D-Wash. "But we have to do a better job at crafting these trade agreements, they cannot be giveaways to the biggest companies."

Jayapal's district — which encompasses the headquarters of pro-trade Amazon — is one that could be in Republican operative Cox's sights as Trade Works for America expands its outreach to 50 districts in the coming months.

In its first two weeks, the campaign has generated 50,000 calls and emails to lawmakers in more than two dozen districts.

"This process will be 'always on' until the vote is taken," Cox said.