Concluding talks over revisions to the North American Free Trade Agreement with Canada and Mexico in August would not be unreasonable, U.S. Trade Representative Robert Lighthizer told lawmakers.

"My hope is that we will before very long have a conclusion with respect to Mexico and that, as a result of that, Canada will come in and begin to compromise," Lighthizer said during a Senate Appropriations subcommittee hearing.

Lighthizer based his timeline on the assumption that Mexican President Enrique Pena Nieto would sign a new agreement with the consent of Andres Manuel Lopez Obrador, Mexico's president-elect, who will be inaugurated Dec. 1. Under U.S. law, the administration must notify Congress at least 90 days before signing a new agreement.

The signatures of U.S., Canadian and Mexican leaders would require "some kind of a conclusion during the course of August," Lighthizer said. "My sense is that that's not an unreasonable time frame if everybody wants to get it done."

House Speaker Paul Ryan said earlier this year that lawmakers would not be able to consider a new NAFTA in 2018 if Congress had not received a notice of intent to sign a deal by May 17.

Sunset dispute

Senators on the committee were split at the prospect of a sunset review clause being included in the new NAFTA framework. West Virginia Democrat Joe Manchin, who has said he supports President Donald Trump's ultimate goal of securing better and more fair trade deals, floated a sunset clause as a way to determine whether a deal actually functioned as intended.

"I would think that after about five years you should have a review: Did it meet the intent of what we did the deal for?" Manchin said. "We don't want to do any harm to anybody in the United States."

Tennessee Republican Sen. Lamar Alexander balked at the suggestion of a sunset provision, warning Lighthizer that it could cost the administration Republican support.

"There are a substantial number of Republicans, including me, who are not likely to vote for any new NAFTA agreement that includes a sunset clause because we don't think it's worth anything," he said. "I would hope you would take that back to the negotiations and hope that presents a real obstacle to having a sunset clause in any final NAFTA agreement."

Alexander also pressed Lighthizer to equalize car and truck tariffs in both the U.S. and the European Union. Lighthizer said that scheme would disproportionately benefit the European Union.

"In my opinion, you can't cherry-pick – you have to be careful of cherry-picking specific products like cars or trucks," Lighthizer said. "You have to do not just trucks and cars, which I believe would greatly favor the European Union in the case that you bring as opposed to the United States, but there are a lot of other manufacturing products that would greatly benefit the United States, and agriculture for sure."

Regarding steel and aluminum tariffs against Mexico and Canada, Lighthizer said the administration hopes they would be resolved in the course of NAFTA talks.