(Reuters) - U.S. lawmakers and economists are awaiting a key analysis of the economic impacts of the new North American trade deal, expected to be published late on Thursday and to show minimal gains at best for the United States.

FILE PHOTO: Flags are pictured during the fifth round of NAFTA talks involving the United States, Mexico and Canada, in Mexico City, Mexico, November 19, 2017. REUTERS/Edgard Garrido

The report from the U.S. International Trade Commission is a crucial step in the push for Congress to consider ratification of the U.S.-Mexico-Canada agreement (USMCA), the first new trade pact secured by the administration under President Donald Trump.

Trump has said bad trade deals have cost millions of American jobs, and promised repeatedly to overhaul them on the campaign trail.

The trade commission’s report has been kept under wraps and will be used by U.S. lawmakers to help decide whether to support USMCA, which would replace the North American Free Trade Agreement (NAFTA) that came into force in 1994.

The administration is preparing a public relations offensive, as an analysis showing little or no U.S. gains from the changes would be a setback for Trump and give some Democrats an excuse to deny him a major political victory.

The renegotiation of NAFTA marked a major victory for Trump, who wanted to increase domestic jobs through more restrictive trade with Canada and Mexico and still salvage the three-country, $1.2-trillion market.

The report will measure the projected impacts of the changes on the U.S. gross domestic product, as well as areas more difficult to evaluate such as new rules of origin, intellectual property protections or elimination of non-scientific food safety barriers.

“The big question is what the report will say the actual gains are. I don’t think they are going to be big, because we already have a good agreement,” said Inu Manak, a trade specialist at the Cato Institute, a conservative think tank in Washington.

One major question is whether tighter regional content rules for the automotive sector will be viewed as positive or negative in the report. In October, the U.S. Trade Representative’s office touted the changes to the rules of origins as expected to preserve jobs and incentivize “up to billions annually.”

The USTR also highlighted changes on intellectual property rights, comprehensive enforcement provisions, and improvements for U.S. dairy and poultry producers.