Immigration activists hold a banner and placards during a rally calling for immigration reform at Lafayette Square in Washington, DC on November 3, 2014
Washington (AFP) - US Senate Democrats blocked a controversial bill Tuesday that would fund homeland security but derail President Barack Obama's immigration plan, plunging Congress into an impasse as a funding deadline looms.
In December, lawmakers funded all federal departments through the end of fiscal year 2015 except for the Department of Homeland Security, which it funded only through February 27 so the new Republican-controlled Congress could put brakes on Obama's plan to shield millions of undocumented workers from deportation.
But Senate Democrats united to block the bill from advancing in their chamber, arguing they do not want to see the $40 billion in critical funding held hostage to to political brinkmanship.
"We are happy to debate homeland security, but not with a gun to our head or to the president's head," Democratic Senator Chuck Schumer said shortly after the vote.
The battle over DHS funding has become one of the most turbulent congressional debates of 2015, with Republicans irate over what they describe as presidential overreach, and most Democrats lining up behind Obama, who has threatened to veto the legislation.
Last month, the House passed the bill funding DHS through September, but attached five riders that would strip Obama's authority to carry out his executive action on immigration.
Blocking the bill's advancement forces lawmakers to craft a compromise in barely three weeks, pass a "clean" DHS funding bill, or see parts of the department that oversees border security, cyberterrorism prevention and the US Secret Service which protects the president go into partial shutdown.
Democrats oppose the bill's "poison pill" immigration inserts, and insist on passing a straightforward DHS funding bill.
"If my colleagues want to fix our broken immigration system, we are happy to have a debate," Democratic Senate Minority Leader Harry Reid said of Republicans.
"But we should not put our national security at risk in the meantime."
Senate Majority Leader Mitch McConnell acknowledged the vote was largely about challenging Democrats and their support for the president while he "repeatedly reached beyond his authority."
He called Democratic opposition to the bill an "absurd position" that jeopardizes funding for vital security programs.
McConnell in the end voted against the measure for procedural reasons, but one Republican, Dean Heller, joined Democrats in opposition.
Senator John McCain said he and fellow Republicans were weighing options for the path forward.
"I'm not sure exactly what I'd support, but I do not support shutting down DHS," he told reporters.
"This is going to be a real moving target here for the next week or so... but the object must be not to shut down the government."
Obama on Monday visited DHS, where he urged Republicans not to play chicken over federal spending.
He warned that failure to fund DHS would mean paychecks halt for 40,000 border patrol agents, 50,000 airport screeners and 13,000 immigration officers.