The U.S. Senate overwhelmingly voted on Tuesday to begin consideration of a White House-backed bill to overhaul the U.S. immigration system, burying a procedural roadblock that opponents regularly use to delay or kill legislation.
With last November's election indicating broad support for the landmark measure, even some senators who have expressed opposition voted to allow the debate and amendment process to commence.
By a vote of 82-15, the Senate cleared the way for consideration of the measure that could stretch through the end of this month.
Foes quickly offered amendments to change or even kill it.
Republican Senator Charles Grassley of Iowa introduced a plan to require the Obama administration to certify "effective control over the entire southern border" for a period of six months before any of the 11 million undocumented residents in the United States could begin applying for legal status.
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"Border security first, legalize second," Grassley said.
The legalization and ultimate citizenship for the 11 million is a central component of the bill. Democrats and some Republicans have vowed to block any measure that leaves their fate in doubt indefinitely.
Senate Judiciary Committee Chairman Patrick Leahy, a Vermont Democrat and a chief supporter of the bill, filed three amendments, including one to provide to lawfully married same-sex couples protection that other spouses now enjoy.
The measure would allow U.S. citizens to seek permanent resident status - a green card - for a foreign same-sex partner.
"Seeking equal protection under our laws ... is the right thing to do," said Leahy. The liberal Democrat had pulled the amendment from consideration by his panel last month, knowing it did not have enough support to be added to the bill.
Nearly 50 amendments had been filed by late Tuesday.
The first of them could be voted on as early as Wednesday if Democrats and Republicans reach a deal on how to proceed with them.
Earlier on Tuesday, President Barack Obama sought to inject momentum into the push for immigration reform.
"If you genuinely believe we need to fix our broken immigration system, there's no good reason to stand in the way of this bill," Obama said at the White House just hours before the Senate staged its first vote on the measure.
"If you're serious about actually fixing the system, then this is the vehicle to do it," he said.
Obama, who won re-election last year thanks in part to strong support from Latino voters, has made immigration reform a top priority of his second term.
He had not given a major public address on the issue for some time, reflecting a White House strategy of not wanting to get in the way of the bipartisan bill's progress in the Senate.
Obama's speech on Tuesday was the first major departure from that strategy.
The Senate bill would authorize billions of dollars in new spending for enhanced border security and create new visa programs for high- and low-skilled workers in addition to providing a pathway to citizenship for the 11 million undocumented immigrants - many from Mexico and Central America.
As Congress plunged into a contentious debate on the bill, Senator Tim Kaine of Virginia, a Democrat, delivered a Senate speech in support of the bill in Spanish.
Senate officials said it was the first time in at least decades that a floor speech was spoken entirely in a language other than English.
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The bill, which has broad support from Obama's Democrats, will need backing from some Republicans in order to give it momentum in the more conservative, Republican-controlled House of Representatives, where the pathway to citizenship provisions face deeper skepticism.
Four Republicans joined with four Democrats in writing the Senate bill earlier this year.
In a sign of the hurdles to come, House Speaker John Boehner of Ohio said he expected immigration reform to be law by the end of the year. But he said the Senate measures to enforce the changes and secure the U.S. border with Mexico were inadequate.
Senate Republican leader Mitch McConnell of Kentucky warned in a speech in the Senate: "In days ahead there will be major changes in this bill if it is to become law."
Immigrant groups fear that too many changes could erode a delicate coalition now pushing the bill.
Boehner, the top Republican in Congress, told ABC television in an interview that aired on Tuesday: "I've got real concerns about the Senate bill, especially in the area of border security and internal enforcement of the system. I'm concerned that it doesn't go far enough."
Boehner added that reforming the immigration system was his top legislative priority this year.
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"I think by the end of the year we could have a bill," he told ABC. Asked if that bill would be one to also pass the Democratic-led Senate and be signed into law by Obama, Boehner said: "No question."
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