Well that should just about wrap that up:

Of all the endorsements in the Democratic Party, [Ted] Kennedy’s is viewed as among the most influential. The Massachusetts senator had vowed to stay out of the presidential nominating fight, but as the contest expanded into a state-by-state fight — and given the tone of the race in the last week — associates said he was moved to announce his support for Mr. Obama.

(He probably just watched this great video.)