AP Photo/Pat Sullivan

Vice President Joe Biden got a hero's welcome today at the NAACP Convention in Houston, one day after rival Mitt Romney was booed during remarks before the same group.

And while the VP did not directly address treatment of the presumptive GOP nominee, he suggested the frosty reception was not misguided, warning that Romney and Republicans are threats to the group's reason for existence.

"On civil rights, your raison d'etre, the reason for our existence," Biden said, "I want to remind everybody of one thing: Remember, remember what this [organization], at its core, was all about… It was all about the franchise. It was about the right to vote. Because when you have the right to vote, you have the right to change things."

"Did you think we'd be fighting these battles again?" he questioned, alluding to efforts by Republicans to impose more stringent voting requirements in states around the country.

"I didn't think we'd be back. I remember working with Republicans - and by the way, this ain't your father's Republican Party - remember working with Republicans on motor-voter, on expanding the franchise on early voting, on voting by mail. Some of these were Republican ideas. But this is not the Republican Party here today, nor Romney's.

Get more pure politics at ABC News.com/Politics and a lighter take on the news at OTUSNews.com

"They see a different future, where voting is made harder, not easier," he said, "where the Justice Department is even prohibited from challenging any of those efforts to suppress votes."

"Folks, there's a lot more to say, but this is preaching to the choir," Biden concluded before the adoring crowd.

Biden used his address, billed as a campaign speech, to energize the African-American constituency that overwhelmingly backs Obama and Democrats and may play a crucial role in a handful of battleground states in November.

He offered a full-throated defense of the administration's signature accomplishments, hailing the 2009 auto bailout as "not popular but it was critical"; the call to target Osama bin Laden as a "bold decision with profound risks;" and the health care law that "required [Obama] early on to use up all of his political capital" but which led to historic benefits for African-Americans.

The VP also suggested there has been a conspiracy to obstruct Obama from the beginning of his term, citing the lack of Republican support for the Recovery Act, the health care law, the Lilly Ledbetter Fair Pay Act, and the debt ceiling debate last summer.

"Their discipline is amazing. They have never let up. But neither has my guy, neither has Barack Obama," he said. "He has not given up. He continues to be driven by the character of his convictions. Folks, in the end, that's what the presidency is all about."

President Obama, who had faced some criticism for not attending the convention, delivered a video message, telling NAACP members, "I stand on your shoulders. And at the NAACP you have always believed in the American promise, that idea that no matter who you are or what you look like or where you come from, America is the place where you can make it if you try."