Democrat John Edwards has given his long-awaited endorsement to Barack Obama.

It's a major boost from a former presidential rival as Obama tries to shrug off Hillary Rodham Clinton, who is determined to press ahead.

Edwards was to appear with Obama in Grand Rapids, Mich., as Obama campaigns in a critical general election battleground.

The endorsement comes the day after Clinton defeated Obama by more than 2-to-1 in West Virginia. The loss highlighted Obama's work to win over the "Hillary Democrats" -- white, working-class voters who also supported Edwards in large numbers before he exited the race.

Edwards, a former North Carolina senator and the 2004 vice presidential nominee, dropped out of the race in late January.