Civil rights leader and U.S. Rep. John Lewis abandoned support for Hillary Rodham Clinton’s presidential bid Wednesday in favor of Barack Obama.

The Democratic congressman from Atlanta had been the most prominent black leader in Clinton’s campaign - and is now its biggest loss.

It’s more than just a blow to Hillary’s morale. John Lewis and nearly 800 other superdelegates get a vote at this summer’s national convention.

Clinton enjoyed an edge in superdelegates support since the beginning of time. But slowly, even that is starting to erode in Obama’s favor.

Many are uncommitted. None want a brokered convention. To avoid mass hysteria, superdelegates are likely to back a clear favorite the instant there is one.

Victories in next Tuesday’s Ohio and Texas primaries could trigger a large-scale defection that paves Obama’s way to the Democratic nominations.

John Lewis said Obama “represents the beginning of a new movement in American political history” and he wants “to be on the side of the people.”

“After taking some time for serious reflection on this issue, I have decided that when I cast my vote as a superdelegate at the Democratic convention, it is my duty … to express the will of the people,” he said.

Appropriately, this photo captures U.S. Rep. John Lewis standing between Sen. Barack Obama and Sen. Hillary Clinton. Lewis now supports the former.

As one of the prominent civil rights leaders of the ’60s, Lewis’ support had been a coveted prize among the Democratic candidates.

“John Lewis is an American hero and a giant of the civil rights movement, and I am deeply honored to have his support,” Barack Obama said in a statement.

Clinton frequently cited Lewis in trying to establish her credentials among minority voters, calling her campaign as a continuation of his work.

But Lewis felt pressure to get behind Obama after his district supported the Illinois senator roughly 3-to-1 in Georgia’s Super Tuesday primary.

Lewis’ change of heart follows a similar move by Georgia Rep. David Scott, a black Democrat who represents a neighboring district.

Also yesterday, another superdelegate, Sen. Byron Dorgan of North Dakota, endorsed Obama, citing the presidential hopeful’s record on trade.

Earlier this week, former White House hopeful Sen. Chris Dodd backed him as well. Clinton is endorsed by 13 Senate colleagues, Obama 10.