President Obama pledged on Wednesday to not "walk away" from immigration reform during a speech to the Congressional Hispanic Caucus.

The president acknowledged disappointment over his failure to pass a comprehensive immigration reform bill over in the past 18 months, and urged Republicans who'd previously backed reform to join with Democrats to pass a bill.

"Now, I know that many of you campaigned hard for me, and you’re disappointed we haven’t been able to move this over the finish line yet. I am too," Obama told the CHC at its gala dinner. "But let me be clear: I will not walk away from this fight.  My commitment to getting this done as soon as we can is real."

Obama had signaled occasionally during his months in office that he would move to advance an immigration bill. Sen. Scott Brown (R-Mass.) said in April that Obama had called him about immigration, which the president had told Brown was next on the agenda.

Many Republicans who'd supported comprehensive reform, which President George W. Bush had pushed in 2007, have now backed off their position. Sen. John McCainJohn Sidney McCainLawmakers worry about rise of fake video technology Democrats put Dreamers and their party in danger by playing hardball Trump set a good defense budget, but here is how to make it better MORE (R-Ariz.) has called for tougher immigration restrictions in a primary cycle during which incumbent Republican senators have faced conservative primary challenges.

Obama acknowledged this, and leaned on GOP senators to support the legislation.

"Today, the folks who yell loudest about the federal government’s long failure to fix this problem are some of the same folks standing in the way of good faith efforts to fix it," he said. "And under the pressures of partisanship and election year politics, most of the 11 Republican senators who voted for that reform just four years ago have backed far away from that vote today."

"Without the kind of bipartisan effort we had just a few short years ago, we can’t get these reforms across the finish line. But their leadership has made reaching 60 votes the norm for nearly everything the Senate has to do," the president added. "And the American people’s business is on hold because, simply put, the other party’s platform has been 'no.'"