Commerce Secretary Wilbur Ross said Tuesday the current talks to renegotiate the North American Free Trade Agreement could stretch on into the fall, suggesting the U.S., Canada, and Mexico remain far apart on some key issue despite their previously optimistic assessments.

“NAFTA, like any trade negotiation, started with easier topics then deals with more difficult, more complex, more important ones. We’re now in that later on phase,” Ross said at a Los Angeles conference. He said he hoped they would be finished by midsummer, but added they could “take until fall, and who know what happens then … As you move toward the middle of year, the political calendar makes it difficult.”