If Canada’s not part of the deal, Trump could forfeit his ability to get a straight up-or-down vote in Congress without any amendments under trade promotion authority legislation.

Trump notified lawmakers in 2017 of his intention to renegotiate NAFTA, not strike a bilateral trade deal with Mexico. So, unless Canada is brought into the pact, he could be challenged on whether he has actually met the requirements of the TPA legislation, said Bill Reinsch, a senior adviser at the Center for Strategic and International Studies.

That’s probably more likely if Democrats win control of the House, since they are loathe to give Trump a major victory on any issue, Reinsch said.

House Minority Leader Nancy Pelosi derided Trump’s comment that he want to change NAFTA’s name because it had “a lot of bad connotations” with the American public.

“American workers don’t need NAFTA with a new name,“ she said in a statement. “While I am ever hopeful of a successful trade agreement, the Trump administration has a very poor record when it comes to truly delivering substantive progress after claiming breakthroughs with other nations.“

But even some Republicans, including Sen. Pat Toomey, are warning Trump not to withdraw from NAFTA before he has won congressional approval of a new deal involving all three countries.

“To use Trade Promotion Authority’s ‘fast-track’ procedures, the administration must also reach an agreement with Canada,” the Pennsylvania senator said in a statement. “Conversion into a bilateral agreement would not qualify for TPA’s ‘fast track’ procedures and would therefore require 60 votes in the Senate.”

Toomey also said he had “serious concerns” about several provisions of the agreement, including ones that would weaken investor protections and require 40 to 45 percent of an auto to be made by workers earning more than $16 per hour to qualify for duty-free treatment. That provision, which is seen as a sop to organized labor, is aimed both at raising wages in Mexico and encouraging more production in the United States.

Even if leaders of the three countries sign the deal in November, as the administration currently hopes, the U.S. International Trade Commission still must complete an economic analysis before Congress can approve it. That could push any vote well into 2019. If Republicans fare badly in the upcoming election, they could feel less beholden to Trump and less likely to support an agreement that contains provisions at odds with years of Republican trade policy, Reinsch said.

U.S. Trade Representative Robert Lighthizer said he hopes tougher labor provisions in the U.S.-Mexico deal will win over Democratic lawmakers who have opposed previous trade agreements. But after Monday’s announcement, major union groups said they still needed to review the details and few Democrats rushed forward to endorse the pact.

“Any new NAFTA must raise wages for American workers, get rid of the current agreement’s outsourcing incentives and put working families ahead of special interests and big corporations,” said Rep. Rosa DeLauro (D-Conn.), who led House opposition that almost succeeded in denying former President Barack Obama new trade promotion authority in 2015.

Rep. Sandy Levin (D-Mich.) also said he was skeptical the deal contained reforms he has long championed. “Unfortunately, Members of Congress have not seen the reported agreement, despite statutory requirements for full consultation. But reports to date leave major questions about the specific rights of workers to overturn the thousands of unfair ‘protection’ contracts now in place in Mexico, as well as the mechanisms to effectively enforce these rights,” he said.

Another key Democrat, Rep. Richard Neal (D-Mass.), said that the parties needed to fix the original pact’s shortcomings by ensuring obligations are “both enforceable and enforced. Otherwise, the efforts of the past year risk amounting to little more than re-arranging the deck chairs on the Titanic.” Neal is in line to become chairman of the powerful House Ways and Means Committee if Democrats win control of the House in November.

Trump made the renegotiation of NAFTA a central issue of his campaign, threatening to tear up the pact unless Canada and Mexico agreed to new terms. But once in office, he discovered strong opposition in Congress to terminating the agreement and disrupting a trade relationship built up over the last 24 years, especially without a new deal to take its place.

U.S. negotiators initially hoped to forge a new trilateral deal before the end of 2017, just a few months after talks began. After missing that and a series of other informal deadlines, including the July 1 Mexican election, the Trump administration began focusing its efforts on reaching a deal with Mexico before solving remaining issues with Canada.

That became the top priority so outgoing Mexico President Enrique Peña Nieto could sign the pact before leaving office on Dec. 1, thereby sparing incoming Mexican President Andrés Manuel López Obrador the burden of finishing talks on the pact.

But in order for Peña Nieto, Trump and potentially Trudeau to sign the pact in late November, Lighthizer is intending to send Congress a letter on Friday providing the statutorily required 90-days notice.

That puts pressure on Canada to resolve its issues with the United States in the next few days or risk being left out.

Reinsch said he saw a 60 percent chance of Canada reaching a deal this week, although several big issues involving government procurement and government-to-government dispute settlement appear to still be up in the air.

If the talks drag on, there is probably still an 80 percent chance Canada will reach a deal by the time the pact is signed in November, which would keep NAFTA a trilateral deal and resolve the issue of whether the Trump administration followed procedure, he added.

Meanwhile, both business and labor groups have begun picking apart Monday’s agreement. The Business Roundtable, which is made up of CEOs of leading U.S. corporations, expressed reservations about a new clause that could potentially terminate the agreement after 16 years. However, that is a watered-down version of the five-year “sunset review” mechanism the Trump administration initially sought.

BRT and the U.S. Council for International Business also expressed concern over the weakening of investment protections for some business sectors — a move that could help the Trump administration pick up Democratic support, but that might keep major business groups from aggressively lobbying for the pact.

One provision of the new agreement that the Trump administration hailed as a major victory would require cars to contain 75 percent U.S. and Mexican content to qualify for zero duties under the agreement. That’s up from 62.5 percent currently.

A group representing Ford, General Motors and Fiat Chrysler said it was generally “optimistic” about the new auto “rules of origin,” but still had to review them in detail.

However, another larger auto coalition representing both U.S. and foreign-brand manufacturers raised concern about Trump’s threat to withdraw from NAFTA and replace it with the new U.S.-Mexico agreement.

“It is unclear how withdrawal from NAFTA” would allow the U.S. auto industry to remain competitive in world markets, said John Bozzella, president and CEO of Global Automakers and spokesman for Here For America. “Canada’s participation is crucial, and we continue to urge all three governments to modernize NAFTA in ways that benefit American auto workers and consumers.”