Congressional leaders and rank-and-file lawmakers on both sides expressed caution Monday about the Trump administration's deal to replace the North American Free Trade Agreement, saying they need to learn more details about the agreement.

President Trump conceded Monday that it was uncertain whether Congress would approve the deal.

"I'm not all confident. I don't know," Trump said of the deal's prospects in Congress at a Rose Garden event to announcement the agreement, known as the U.S.-Mexico-Canada Agreement, or USMCA. He noted that it was possible the deal wouldn't get a vote until next year, at which point Democrats could control one or both chambers in Congress.

"They might be willing to throw [away] one of the great deals for people and the workers. They may be willing to do that for political purposes, because, frankly, they will have 2020['s presidential election] in mind," Trump said.

Under the Trade Promotion Authority that delegates power to the administration to negotiate trade deals, lawmakers have 60 days to approve the deal once submitted. Amendments are not allowed, so lawmakers can only vote on accepting or rejecting it.

The main provision of the deal alters the so-called "rules of origin" under NAFTA by setting at 75 percent the amount of North American-made parts needed for a car or truck to be duty-free under NAFTA, up from 62.5 percent. It also requires that at least 40 percent of all auto content be made by workers making at least $16 an hour or its equivalent. It also opens up more of Canada's dairy market to U.S. farmers, a key concern for agricultural interests in states like Wisconsin and New York.

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Congressional lawmakers on both sides said the outlines of the deal were good, but stated that it lacked enough specifics to state a definitive conclusion. House Speaker Paul Ryan, R-Wis., who is retiring from Congress, withheld an endorsement, saying he had to be certain about the agricultural provisions. "I look forward to reviewing the text of the agreement, particularly the dairy provisions, and engaging with members and stakeholders on the details,” he said. A spokeswoman declined to elaborate, saying they were still poring over the text.

Other Republicans gave it a tentative thumbs-up, provided that home-state industries didn't have an objection. "I appreciate the administration working to make certain these markets remain available to Kansas farmers, ranchers, and manufacturers, providing them some much-needed certainty," said Sen. Jerry Moran, R-Kan. "I will further analyze the details of this agreement, but this announcement is clearly a positive development."

Democratic leaders were similarly circumspect, though many have called for some of the deal's provisions, like tighter rules of origin, in the past. "Two areas where I particularly want to see the details are dairy, where our dairy farmers are being taken advantage of by Canada, and real enforcement of labor provisions," said Senate Democratic Leader Chuck Schumer, D-N.Y. "Labor provisions are good, but too often they are written into trade bills and never enforced."

House Democratic Leader Nancy Pelosi, D-Calif., said her party would "closely scrutinize the text."

However, Democrats largely refrained from attacks and praised the administration's intentions. "I appreciate United States Trade Representative [Robert] Lighthizer’s sustained efforts to address some of these concerns throughout this renegotiation," said Rep. Rosa DeLauro, D-Conn., a key Democrat on trade issues. "Still, we must reserve final judgment until we have a full and clear understanding of all the details."