Washington (CNN) -- President Barack Obama tried Tuesday to build momentum for an immigration reform bill that later passed a key Senate hurdle, saying the measure was a commonsense approach to fix a broken system that has allowed 11 million people to live illegally in America.
At a White House event a few hours before the Senate voted to debate the plan, Obama emphasized that it would increase spending on border security and require undocumented immigrants to pursue what he called an "arduous" path to eventual citizenship.
"You have to pass background checks, you have to learn English, you have to pay taxes and a penalty and then you have to go to the back of the line behind everybody who has done things the right way and have tried to come here legally," Obama said in addressing a major complaint by Republican opponents who call the reform measure an amnesty.
The legislation addresses an emotionally charged issue with huge political stakes for both parties. However, fierce opposition by conservatives may prevent it from getting through Congress despite years of negotiation and major compromise.
In the Senate, Republicans who forced the procedural step that required at least 60 votes to launch debate on the immigration bill joined Democrats to easily surpass the threshold.
The final tally was 82-15, but Senate Majority Leader Harry Reid warned that some Republicans had no intention of supporting the measure even though they supported opening the formal debate.
Under the bipartisan proposal hammered out by the so-called "Gang of Eight" senators this spring, most undocumented immigrants would face a 13-year path to citizenship.
Polls show many Americans also favor some form of immigration policy overhaul, depending on the details of legislation.
Obama and congressional Democrats are anxious to fulfill a long-delayed pledge to Latino voters to pass reforms to the troubled immigration system. Passage could pay political dividends for their party for many years.
Republicans are in a more difficult bind.
Latinos backed Obama over Mitt Romney by a 44-point margin in November and GOP strategists are concerned about the party's long term viability in national elections if that trend is not reversed.
Some congressional conservatives say opposing the "Gang of Eight" plan is a matter of principle and they won't bend. They remain skeptical about any measure offering a path to citizenship. A lot of them consider it amnesty.
That provision, coupled with concerns about whether the bill really will tighten security along the nation's porous borders as proposed, may make it difficult for conservatives to support -- especially those up for re-election next year.
"The bill grants permanent legal status to millions of undocumented immigrants, as currently written, without really any guarantee of securing the border. Now, how would that possibly be a good idea?" asked Sen. John Cornyn of Texas, the chamber's No. 2 Republican, who voted Tuesday for opening debate.
Sen. Marco Rubio, R-Florida, a member of the bipartisan "Gang of Eight" who is considered a possible GOP presidential contender in 2016, argued that doing nothing amounts to what he called a "de facto amnesty" for immigrants currently living illegally in America.
Even if the Senate passes the legislation, strong opposition from conservative Republicans in the House makes final prospects uncertain.
Rubio, a popular conservative of Hispanic descent, has made clear that border security requirements must be toughened if he and other GOP skeptics will support it.
He is pushing an amendment that would make Congress, not the executive branch, responsible for deciding if security metrics at the border have been met before other aspects of the reform bill -- including the pathway to citizenship -- are triggered.
Because Rubio's support is so critical, other members of the bipartisan group have hinted they likely will back his proposal even though they are reluctant to make major changes to their original compromise.
The vote on the Rubio amendment will be one of the most closely watched as floor action unfolds over the next three weeks.
It's not clear when that vote will take place. But there will be many other amendments related to stepped up security checks of people entering the country, temporary visas for high and low skilled workers, and other technical provisions.
Republican opponents are expected to offer amendments to undermine the plan and weaken support.
"Gang of Eight" members have vowed to work together to defeat those amendments and prevent key parts of the agreement from crumbling.
"Senators will propose a number of ideas to make the legislation better. Some will offer ideas to make it worse. But those suggestions must preserve the heart of the bill," said Reid, a Nevada Democrat.
Advocates for comprehensive reform won the first major legislative victory last month when the Senate Judiciary Committee voted 13-5 to approve the "Gang of Eight" plan.
Democratic leaders hope to have a vote on final passage by the end of June.
A bipartisan group has been working on an immigration plan in the House but the effort suffered a setback last week when a key member dropped out of the negotiations.
Previous efforts to pass immigration reform fell short last decade even though it was said to be a priority of President George W. Bush at the time.