President Donald Trump's top economic adviser, Larry Kudlow, said he is not optimistic that negotiators can reach a deal on a new version of the North American Free Trade Agreement, or NAFTA.

House Speaker Paul Ryan said a NAFTA deal must be sent to Congress by Thursday for it to be passed this year.

If a new NAFTA deal is not passed this year, political changes could endanger any new agreement.

Larry Kudlow, President Donald Trump's top economic adviser, said he is skeptical of the chances negotiators agree on a new version of the North American Free Trade Agreement.

In an interview with Politico's Ben White and Nancy Cook, Kudlow said a tight deadline would make it difficult to seal the deal.

"I don’t know if we are going to get a deal," Kudlow said. "You are talking to the guy who is the optimist and the happy warrior, and as we meet now, I don’t know."

Trump began the process of renegotiating the 24-year-old trade deal days after taking office. Formal negotiations among the US, Canada, and Mexico started in August. While the three countries say they are getting closer to a deal, the Trump administration's method for renegotiation — known as Trade Promotion Authority, or TPA — has put a squeeze on the timeline.

TPA mandates a review period for Congress. House Speaker Paul Ryan said at a conference Tuesday that Congress would need a new NAFTA agreement in its hands by May 17 for it to be approved in 2018. After that point, the deal would be reviewed by lawmakers elected in the 2018 midterms, which could change the makeup of Congress.

The political reality and tight window raised concerns among Trump administration members, including Kudlow. During a speech earlier this month, US Trade Representative Robert Lighthizer said negotiations would be on "thin ice" absent a review from the current Congress.

Kudlow, who generally favors free trade and maintains an upbeat attitude about the economy, could not muster that positive outlook while talking to Politico.

"I don’t even want to go with the usual Kudlow optimist. I can’t go there," Kudlow said.