LAS VEGAS, Nev. – If the White House needs a surrogate who can pivot punch a rival’s policies to delivering bawdy humor about his parents, they’ve got their man.

Speaking to 1,800 Latino activists at the National Council of La Raza annual conference, Vice President Joe Biden challenged presidential rival Mitt Romney to release his tax returns, linking the Republican's lack of financial disclosure to his party's support for strict immigration laws.

"He wants you to show your papers but he won't show us his," Biden said to laughter from the pro-immigration crowd, which also cheered his descriptions of the administration's support for the Dream Act.

Biden, who likened discrimination against new Latino immigrants to the xenophobia aimed at Irish Catholics who immigrated to the United States after the potato famine of the mid-1800s, said he grew up in a multigenerational household similar to those of many middle-class Latino families.

That prompted a reference to the age-old problem of couples sharing a household with older family members.

"Those walls were awful thin, I wondered how the hell my parents did it," Biden said. "That's a different story. I know you don't know anything about that!"

Shifting between jocular to passionate, Biden warned that Romney and Republicans "don't get" the middle class mentality, saying that conservative ideals could erase decades of progress for minority populations if Romney names new judges to the Supreme Court.

"Imagine the court with two more [Antonin] Scalias and two more [John] Roberts on the court," he said. "Imagine what it would be like. Imagine what it will mean for civil rights, voting rights, and so much more that we've fought so hard for so long to accomplish."

Although Chief Justice Roberts was the swing vote in favor of upholding most of President Obama’s health care law, he is generally regarded as being conservative.

"Imagine a Justice Department that supports rather than challenges the continued efforts to suppress the right to vote," the vice president said, offering praise for embattled Attorney General Eric Holder.

Biden urged the audience to get involved in the presidential election, noting the "talent" and "patriotism" of the Latino community in America -- also a key voting bloc for both sides in the November contest.

"This is your moment," Biden said. "This is the moment for your community."

Tuesday’s address was the first of two major conference speeches for Biden this week; he travels to Houston Thursday to speak to a convention of the NAACP.