Republicans backed Obama's bid for the trade authority, but many Democrats felt betrayed by the measure's failure to punish currency manipulation or include protections for American workers impacted by globalization.
The bill would have allowed Obama to submit the Trans-Pacific Partnership (TPP) currently under negotiation, and an upcoming US-Europe trade pact, to Congress for an up-or-down vote, with lawmakers prevented from making changes.
The White House says it needs such fast-track authority in order to finalize talks with the 11 other nations in the TPP, without the threat of Congress adding amendments once negotiations are complete.
Democrats withdrew their support after Republican Senate Majority Leader Mitch McConnell refused to package the measure with three other trade bills, including one that cracks down on currency manipulation -- seen by many as the key impediment to fair trade.
"We know the global economy is a rough sea, and Republicans are asking us to pass a trade package that forces the American worker to navigate those waters in a leaky boat," said Senator Chuck Schumer, a senior Democrat.
All Democrats but one, Senator Tom Carper, voted against formally opening debate on the measure, a procedure that needed 60 votes in the 100-member chamber but failed 52-45.
"This should be a top priority for Democrats and Republicans," said the pro-trade Carper, who had held a last-ditch press conference extolling the benefits of trade promotion authority.
- Collapse of support -
But Senate Republican John Thune said that the Democrats' abandonement of Obama, who has viewed trade as perhaps the primary legislative goal of his remaining 21 months in office, amounted to "throwing their own president under the bus."
McConnell called the vote "shocking," while labor unions declared it a victory for American workers.
Senate Finance Committee Chairman Orrin Hatch, who co-authored the package of trade bills, expressed astonishment at the collapse of what he described as an agreement to support both executive trade authority and trade adjustment to fund worker assistance programs.
"It's amazing to me that they would do this to the president, on a bill of this magnitude," Hatch fumed.
The vote did not kill the trade authority bill, but only delayed it. McConnell said he intends to bring it up again, perhaps after lawmakers reach agreement on how to proceed with the four trade measures.
That could spell bad news for Obama, who might be forced to swallow unwanted trade enforcement provisions that his administration says would make it hard for TPP partners to sign on.
White House spokesman Josh Earnest said he hoped senators would be able to "work through" the procedural hang-up.
Obama met with 10 Senate Democrats after the vote to discuss the path forward, with the White House saying the president and members remained "committed to continuing work on this important priority."
But Hatch, who insisted that attaching an enforceable currency provision to the TPA bill would doom the Pacific trade accord, voiced dismay, saying "I don't know where we're going to go."
Trade authority supporters say the legislation would require 150 congressional negotiating priorities be met in the trade pact, including provisions on human rights and the environment.
But critics say the accord, under negotiation in secrecy, is a job-killer that prioritizes corporate interests over those of American workers.
"We want more trade, we just want it under very different definitions and very different rules," said Senate Democrat Sherrod Brown, who is helping lead opposition to the Pacific trade deal.
Critics argue that uniting 12 nations in a free-trade zone would prompt a race to the bottom on wages, with the US workforce unable to compete with cheap labor in pact partners like Chile, Peru and Vietnam.
"Trust us to know what's good for workers. This ain't it," said Richard Trumka, president of the AFL-CIO, America's largest labor organization representing 12 million workers.