(CNN) -- Vice President Joe Biden delivered a rousing address to the NAACP in Houston on Thursday, bolstering support for President Barack Obama and drawing sharp contrasts with the Republican Party on civil rights issues.
On the heels of recent voter identification disputes, Biden strayed from his typical campaign speech to zero in on voting rights, arguing that Republicans were making it more difficult for certain group to vote.
By implementing laws requiring voters to present official identification at the voting booth, Biden said, the GOP sees "a different future, where voting is made harder, not easier."
Democrats have said that such laws are politically motivated and intended to suppress minority voting, given that fewer people in minority groups carry government-issued IDs. Republicans, meanwhile, make the case that such laws prevent fraud and protect the integrity of the system.
The issue was a hot topic this week at the NAACP convention, where Attorney General Eric Holder spoke Tuesday and lambasted states that have considered or attempted to implement such laws, including Texas, Wisconsin and Pennsylvania.
Appealing to the group's founding, Biden on Thursday urged the crowd to "remember what (the NAACP) at its core was all about."
"It was about the right to vote, because when you have the right to vote, you have the right to change things," he said.
He called on the crowd to imagine what the Justice Department would look like under a Mitt Romney administration.
"Imagine the recommendations and who he's likely to pick for attorney general or head of the civil rights division," he said, drawing scorn from the audience.
The vice president also touched on a number of other issues, including energy, health care, women's issues and education. In each instance, he compared Obama's policies with those of the Republican Party.
He particularly faulted the GOP for obstructing what he considers key legislation since Obama took office.
"Their discipline is amazing, they have never let up," Biden said, referring to congressional Republicans. "But neither has my guy. Neither has President Barack Obama. He has not given up. He continues to be driven by the character of his convictions."
This was Biden's first time addressing the convention as vice president, the NAACP said.
"The vice president is a longtime friend to the NAACP," said Roslyn Brock, the group's chairwoman. "He has been a strong advocate for justice and equality over his decades of service in the Senate and the White House."
The president will miss the event because of a "scheduling conflict," his campaign said.
"We declined a few weeks ago, and (the) NAACP was pleased (Vice President Joe Biden) was able to attend," an Obama-Biden campaign official told CNN.
The president's schedule for Thursday initially appeared wide open, but a senior administration official confirmed Thursday morning that Obama and the first lady will give an interview to CBS during the day.
However, the president did make a brief appearance in a pre-taped video that ran before the vice president appeared.
"If you keep standing with me ... I know we can arrive there together," the president said after delivering a few lines from his typical stump speech on helping middle-class Americans.
Hilary Shelton, the NAACP Washington Bureau director and a senior vice president in the organization, said the White House never confirmed a visit.
"They were trying to work out something," Shelton said.
As to why Obama could not attend, he added, "It was that something could not be moved. Something was crucial. And unfortunately, they couldn't move it in a way they could get him here this week."
Obama addressed the convention in 2009. Last year, first lady Michelle Obama spoke to the group.
Biden's speech Thursday came one day after Romney was booed during his own remarks at the NAACP convention, when the Republican vowed to repeal the Affordable Care Act, Obama's signature health care law.
In comparison, Biden drew thunderous applause after trumpeting health care reform and emphasized that the law ensures coverage to "8 million black Americans who never would have had insurance."
The one time the crowd gave a negative reaction occurred when Biden began to close his remarks. He received a standing ovation from about half the audience at the end.
Meanwhile, Romney said the negative reaction he experienced Wednesday didn't come as a surprise.
"I think we expected that," he said on Fox Business Network. "I am going to give the same message to the NAACP that I give across the country, which is that Obamacare is killing jobs."
Two African-American members of the House of Representatives found themselves split after Romney's appearance.
"He gets credit for attendance," Rep. Cedric Richmond, a Louisiana Democrat, said on CNN's "The Situation Room." "But perfect attendance doesn't qualify you to be class president. I thought it was a good gesture to go, but I thought his content was lacking."
Rep. Tim Scott, a Republican from South Carolina, also said on "The Situation Room" that he expects Romney to get about 10% of the black vote come November, suggesting the GOP candidate's focus should be on unemployment and home foreclosures.
"African-American unemployment since 2008 is up 40%," Scott said. "Home closures 25%. So what we have is the same message that works for the rest of America, works for the black community, too."
CNN's Dan Lothian, Shawna Shepherd, Shannon Travis and Ed Payne and contributed to this report.