HOUSTON — Vice President Joe Biden urged black voters Thursday to reject a pitch from presumed Republican presidential candidate Mitt Romney, telling the NAACP that a Romney presidency would be a threat to voting rights for African-Americans.

Biden received a warm response from the overwhelmingly Democratic group as he gave a spirited defense of President Barack Obama's first-term record and blasted Romney and congressional Republicans for being obstructionists.

Speaking to the civil rights organization on the last day of its annual convention, Biden was cheered loudly as he reeled off Obama's first-term record, including killing terrorist Osama bin Laden, bailing out the auto industry and signing the health care law.

“He passed the Affordable Care Act, a goal strived for by presidents since Teddy Roosevelt,” he said to cheers. “It required him early on to use up almost all of his political capital. He prevailed where no president had done before.”

The same audience booed Romney on Wednesday when he said he would repeal the health care law.

Obama captured 95 percent of the African-American vote in 2008 and is expected to win it again by a resounding margin in November. But with contests expected to be close in swing states such as Florida, Ohio, Pennsylvania, North Carolina and Virginia, Biden implored his African-American audience to vote in similar — if not greater — numbers this fall.

He called Republicans obstructionists who do not quit.

“Their discipline was amazing,” he said. “They never let up. But neither has my guy, neither has Barack Obama. He hasn't given up.”

Several conventioneers and congressional Democrats in Washington said Romney's remark on the same day that the Republican-controlled House of Representatives voted to repeal the health care law was a calculated move to appeal to Republicans and conservatives.

“He insulted the NAACP by talking about Obamacare and charter schools,” said Deborah Raymond, a 60-year-old retired teacher from San Leandro, Calif. “Biden gave us hope and inspiration to vote for Obama in November. Biden lit it up.”

Romney's campaign dismissed Biden's speech.

“The black American community has struggled with high unemployment under President Obama, and Vice President Biden's speech today offered no new ideas or solutions,” said Romney adviser Tara Wall.

“Mitt Romney will enact policies that will lower taxes, encourage small-business hiring, reform our education system and give all Americans an opportunity to pursue their dreams,” she said.

Biden urged conventioneers to imagine a Romney Justice Department or Supreme Court.

“Remember what this at its core was all about, what this organization at its core was all about,” he said. “It was 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.”

He said Republican moves to require photo identification at polling places, as well as other new voting access laws in more than a dozen states, were obstacles to the ballot box.

The NAACP, along with several other civil rights and civil liberties groups, view the new laws as attempts to suppress the votes of African-Americans, Hispanics, the young, the elderly and the poor — groups that tend to vote for Democratic candidates. It's message Democrats have been pushing to win votes.

“We see a future where those rights are expanded, not diminished,” Biden said, “where racial profiling is a thing of the past, where access to the ballot is expanded and unencumbered. ... They see a different future where voting is made harder, not easier.”

Biden spoke in place of Obama. White House press secretary Jay Carney said that Obama's absence doesn't mean he's taking African-American voters for granted. Obama delivered regrets and remarks to the convention in a video message played before Biden spoke.

Still, some convention attendees were unhappy that the President was a no-show in Houston.

“It bothers me that President Obama isn't coming,” said Geraldine Alexis, 51, an Arizona public school counselor. “He's taking us for granted. He knows we're afraid to vote for Romney. He knows he has our vote.”