President Obama, interviewed on Univision. Carolyn Kaster/AP Photo

President Obama says the "most important" lesson he learned during his first term in the White House is that "you can't change Washington from the inside."

"You can only change it from the outside," Obama said at a "Meet the Candidates" forum hosted by the Spanish-language network Univision.

"That's how I got elected, and that's how the big accomplishments, like health care, got done, was because we mobilized the American people to speak out. That's how we were able to cut taxes for middle-class families," he said.

Obama said that in a second term he would maintain "a much more constant conversation with the American people" to attempt to leverage their support to spur Congress to act on his agenda.

Republican presidential nominee Mitt Romney immediately seized on the remark, calling it a concession by Obama that he failed to change Washington in the way he promised four years ago.

Watch Obama's comments here:

"The president threw in the white flag of surrender. He said he can't change Washington from the inside," Romney told a crowd of supporters at a rally in Sarasota, Fla., immediately after Obama spoke. "We're going to give him that chance in November. He's going outside.

"I can change Washington. I will change Washington. I will get the job done from the inside."

Since he first accepted the Democratic nomination for president in 2008, Obama has spoken regularly about "change" being best affected by outside pressure on government from ordinary citizens.

"As citizens, we understand that America is not about what can be done for us. It's about what can be done by us, together, through the hard and frustrating but necessary work of self-government," he said at the Democratic National Convention in Charlotte, N.C., earlier this month.

"The election four years ago wasn't about me. It was about you. My fellow citizens - you were the change," he said.

Obama echoed a theme he began articulating four years earlier when he accepted the Democratic nomination in Denver.

"The change we need doesn't come from Washington. Change comes to Washington," Obama said at Invesco Field in 2008. "Change happens because the American people demand it, because they rise up and insist on new ideas and new leadership, a new politics for a new time."