The Senate mustered enough votes to begin debate on a so-called, fast-track bill, seen by some as a prerequisite for reaching any free-trade deal with the U.S.
That debate is being watched closely by Canada and other countries seeking to complete negotiations for the Trans-Pacific Partnership pact, which would create a sprawling, 12-nation trade zone.
The legislation moved ahead with a 65-33 vote, enough to override a filibuster. It appeared stuck earlier in the week, when Democrats sided en masse against the bill — and against their president.
The debate has created bitterness between the pro-trade Obama administration and the trade-skeptical Democratic caucus, in a bizarro-realm dynamic where Republicans are the president's biggest backers.
President Barack Obama pushed his own side to back the deal and the parties reached a procedural arrangement that swayed enough Democratic votes to open debate on the bill.
It led to a surreal scene Thursday: Republicans praising their rival-in-chief.
"I'd like to thank the president," said the Republican leader of the Senate, Mitch McConnell.
"No, you're not hearing things. President Obama's done his country a service by taking on his base and pushing back on some of the more ridiculous rhetoric we've heard. ... He should be recognized for it."
The grumbling was on the Democratic side.
The party's left wing is fuming over several aspects of the trade talks — notably the secrecy. Lawmakers being briefed on the negotiations say they can't even take notes from the room. They say business groups are helping shape the text, with little representation from labour.
Their opposition to free trade is longstanding — and a repeat of the dynamic during the NAFTA debate, when Bill Clinton faced down his own skeptical caucus.
Today's anti-trade contingent notes that manufacturing jobs have plummeted by almost one-third in the U.S. since NAFTA came into effect in 1994, with middle-class wages driven down by cheaper overseas labour.
One rust-belt lawmaker accused fellow politicians of abandoning the middle class — allowing tax breaks for companies that ship jobs overseas and imports built on slave wages.
"My state for 14 years in a row — 14 years in a row — had more foreclosures than the year before," Ohio Sen. Sherrod Brown said Thursday.
"That's not because Ohioans are irresponsible. It's because Ohioans have lost so many of these manufacturing jobs. ... I don't think people around this place think very much about the human face of these kinds of decisions."
But defenders of trade say the free flow of goods isn't the culprit. They argue that technology is phasing out manufacturing jobs in wealthier countries. And that per-capita income has continued to grow in the post-NAFTA era, with trade-related jobs paying better than non-trade ones.
A Democratic congressional leader expressed alarm over the length of the fast-track deal: three years, with the possibility of a three-year extension meaning it could be used by a future president.
"This is effectively a six-year ... carte blanche," Nancy Pelosi said.
She said lawmakers want to know what they're voting for. Under a fast-track arrangement, members abandon their right to amend any trade bill the president sends to Congress.
Other countries say that's the only way to negotiate a trade deal. Some, including Canada, are reluctant to complete negotiations under the threat of 535 lawmakers amending the treaty.