A Meaningless Endorsement

Al Gore emailed his endorsement to Obama's email list, naturally. He said:

Over the next four years, we are going to face many difficult challenges -- including bringing our troops home from Iraq, fixing our economy, and solving the climate crisis. Barack Obama is clearly the candidate best able to solve these problems and bring change to America.

Why does his endorsement hold any merit after the only other potential candidate he would endorse already dropped out? It's not like he would endorse McCain and commit political suicide. McCain isn't green. He's closer to blue than green. He's purplish. A deep, reddish purple, but purple nonetheless.