Larry Sabato, professor of politics at University of Virginia and author of A More Perfect Constitution: Why the Constitution Must Be Revised: Ideas to Inspire a New Generation, weighs in in an e-mail:

The Obama-Clinton contest was so close that a couple of dozen factors and events made the difference, including the voters’ latent resistance to dynasty, Hillary’s critical failure to organize the caucus states, John Edwards’ share of the Iowa caucus vote, etc. But I would certainly put the Ted & Caroline Kennedy endorsement of Obama on the list. After Obama’s unexpected New Hampshire loss, Democrats had begun to believe he was a shooting star. The emphatic Kennedy nod caught Democrats’ collective attention and gave Obama the imprimatur of Camelot at precisely the right moment before other key primaries. Just as Republicans always want to vote for the next Ronald Reagan, Democrats seek to crown the next JFK every four years. Voila! Ted Kennedy made the connection obvious for Democrats.