While it has apologized before, Congress never apologized for slavery, USA Today reported Thursday.

"We've seen states step forward on this," said Sen. Tom Harkin, D-Iowa, noting resolutions in Alabama, Maryland, New Jersey, North Carolina and Virginia. "I'm really shocked, just shocked" that the federal government hasn't apologized. "It's time to do so."

Harkin said he and Sen. Sam Brownback, R-Kan., will propose an apology for slavery and subsequent "Jim Crow" laws that furthered racial segregation. Among the bill's backers are Democratic Sens, Hillary Clinton of New York, the party's first female presidential candidate, and Barack Obama of Illinois, the party's first African-American candidate.

A similar House measure introduced in 2007 has 120 co-sponsors.

Congress apologized to Japanese-Americans in 1988 for imprisoning them in camps during World War II, giving each survivor $20,000. In 1993, Congress apologized to native Hawaiians for the overthrow of their kingdom a century earlier. In 2005, the Senate apologized for failing to enact anti-lynching laws.