Republicans, as well as a few Democrats, have long been frustrated by the Obama administration's refusal to approve the Keystone XL pipeline. But the president's decision to delay the project once again has pushed the issue toward a tipping point. In the Senate, more Democrats have joined pro-pipeline forces, and it's entirely possible Congress will soon -- perhaps as early as next week -- take the matter into its own hands and force approval of the project.

On Thursday morning, Democratic Sens. Kay Hagan and Jon Tester agreed to co-sponsor a bipartisan bill by Republican Sen. John Hoeven and Democratic Sen. Mary Landrieu that would give pipeline company TransCanada the go-ahead to start work. Another Democrat, Sen. Mark Warner, signed on in the weeks after the State Department's January determination that the pipeline would have minimal environmental impact. And seven other Democratic senators -- Mark Pryor, Claire McCaskill, Mark Begich, Joe Manchin, Heidi Heitkamp, Joe Donnelly, and John Walsh -- were already co-sponsors. In all, 11 Senate Democrats, some of them facing tough re-election campaigns this fall, have put their names on the pro-Keystone bill.

Together with all of the Senate's 45 Republicans, the Democratic support puts the number of co-sponsors at 56 -- just four shy of the 60 required to stop a filibuster by Majority Leader Harry Reid. And those are just the senators who have actually chosen to sponsor the legislation. Others might join if it actually comes up for a vote.

The new momentum is the result of the one-two punch of the State Department's environmental judgment followed by the president's delay. Once there was no environmental reason to postpone Keystone XL any longer, some Democrats could no longer maintain their opposition.

"When the president came out and said he's not going to make a decision, people recognized that he intends to defeat the project with delays," says Hoeven. "There is a realization that there is never going to be an end to the process."

Would Reid, legendary for his ability to block legislation, actually allow a vote on the Hoeven bill? Reid's spokesman says the top Democrat is indeed "open" to such a vote, and talks are under way on whether to consider it as a stand-alone bill or as part of some other legislation. In any event, the bill is clearly gaining momentum.

Of course, President Obama has threatened to veto it. This week, White House spokesman Jay Carney, while not repeating the veto threat, said Obama believes the approval process must be run by the State Department, not Congress. Obama might soon have to decide whether to back up that belief with a real, not threatened, veto.

Meanwhile, some lawmakers are working on a way to prevent such never-ending delays in the future. In March, the House passed something called the RAPID Act, which would set time limits on the approval process for projects like Keystone XL. (RAPID stands for "Responsibly and Professionally Invigorating Development," which proves lawmakers have not lost their taste for clunky acronyms.)

The act would set a six-month limit for initial environmental assessments of such projects, and then a two-year limit for full-scale environmental impact studies. Under certain circumstances, those periods could be extended, but the bill would set an outer limit of six years for all of the studying and licensing that goes into big projects.

"The Empire State Building, the Hoover Dam, the Pentagon, and even the New Jersey Turnpike were built in less than six years," House Judiciary Committee Chairman Rep. Bob Goodlatte said at a hearing on the measure last July. "Surely litigants can prepare and file lawsuits in less time as well."

The RAPID Act passed the House in March by a 229 to 179 vote. The "ayes" included just 12 Democrats, but sponsors hope the growing frustration with the administration's Keystone delays might extend to their legislation as well.

The public supports the Keystone XL project by a roughly two-to-one margin. Even key Democratic constituencies, like many labor unions, want it to go forward. Yet it has been stopped by the president, a core of anti-pipeline Democrats on Capitol Hill and a few extremely wealthy environmentalist donors pushing them on.

Previous efforts to pass a Keystone bill have fallen short, and Hoeven cautions that a desperate White House lobbying effort might yet stop the new momentum with perhaps a vote or two to spare. But the tide has turned, and the pro-Keystone forces believe they are on the road to victory.

"If we don't get this bill now," says Hoeven, "I think we're going to get it after November."