President Obama said in an interview with Univision airing Tuesday that he "probably" cannot legalize illegal immigrants by executive order -- a decision he might be faced with if Congress fails to pass comprehensive immigration reform.

"Probably not," Obama said, according to a transcript. "I think that it is very important for us to recognize that the way to solve this problem has to be legislative. I can do some things and have done some things that make a difference in the lives of people by determining how our enforcement should focus."

Some on the left have argued that Obama could simply legalize illegal immigrants himself -- pointing to his previous executive order on the matter.

Obama noted his deportations have focused on criminals and that he has signed an executive order exempting young illegal immigrants from deportation.

"But this is a problem that needs to be fixed legislatively," he said. "So I’m not going to speculate on the House bill failing. I’m going to make sure that I do everything I can to help it succeed."

Obama said he remains "cautiously optimistic" that Congress will come to an agreement, and he said any agreement should include a path to citizenship, not mere legalization.

"You know, here in Washington you always have to recognize that things move more slowly than you’d like. It’s always more difficult than you’d like," he said. "But you know, what I’ve found over the last five years if you are persistent and you stay with it, that eventually the right thing gets done."