MIAMI, Fla. - President Obama today said his failure to push comprehensive immigration reform as promised was the biggest failure of his first term but blamed Republicans in Congress for the lack of progress.

Seeeking to appeal to Latino voters at a Univision News forum, the president explained "when we talked about immigration reform in the first year, that's before the economy was on the verge of collapse, Lehman Brothers had collapsed, the stock market was collapsing, and so my first priority was making sure that we prevented us from going into a Great Depression."

In 2008, then-candidate Obama told Univision's Jorge Ramos, who anchored today's event with Maria Elena Salinas, "what I can guarantee is that we will have in the first year an immigration bill that I strongly support and that I'm promoting. And I want to move that forward as quickly as possible."

Today, Ramos repeatedly pressed Obama to acknowledge he had not kept that promise. "I don't want to get lost in translation," Ramos said in Spanish. Today's forum was conducted in Spanish and the questions translated for the president. "You promised… And a promise is a promise. And with all due respect, you didn't keep that promise."

"I am happy to take responsibility for the fact that we didn't get it done," Obama said. "But I did not make a promise that I would get everything done a hundred percent when I was elected as president. What I promised was that I would work every single day as hard as I can to make sure that everybody in the country, regardless of who they are, what they look like, where they come from, that they would have a fair shot at the American dream. And that promise I kept."

The president placed blame squarely on Republicans. "I confess I did not expect - and so I'm happy to take responsibility for being naive here - that Republicans who had previously supported comprehensive immigration reform - my opponent in 2008, who had been a champion of it and who attended these meetings - suddenly would walk away. That's what I did not anticipate," he said, singling out Sen. John McCain, R-Ariz.

"We initiated the meetings, had a series of meetings. And what we could not get was a single Republican, including the 20 who has previously voted for comprehensive immigration reform, to step up and say, we will work with you to make this happen," Obama continued. Asked about the biggest mistake of his first term, the president relented. "As you remind me, my biggest failure so far is we haven't gotten comprehensive immigration reform done, so we're going to be continuing to work on that," he admitted.

Read more here about the Univision Forum .