Several "senior Democratic sources" tell ABC News that John Edwards will endorse Barack Obama tonight at a campaign rally in Grand Rapids, Mich.

A source close to the Clinton campaign said the Edwards camp gave the Clinton folks a heads up.

"Clearly it's upsetting" the source tells ABC. "He brings the workers" to Obama.

"Well I don't think it's good news, but there's a lot of news in this business and we move forward and move past it. It's not great news," a Clinton senior advisor said.