Obama overtakes Clinton in Democratic superdelegates

Obama added superdelegates from Utah and Ohio, as well as two from the Virgin Islands who had previously backed Clinton. The additions enabled Obama to surpass Clinton's total for the first time in the campaign. He had picked up nine endorsements Friday.

The milestone is important because Clinton would need to win over the superdelegates by a wide margin to claim the nomination. They are a group that Clinton owned before the first caucus, when she was able to cash in on the popularity of the Clinton brand among the party faithful.

Those party insiders, however, have been steadily streaming to Obama since he started posting wins in early voting states.

"I always felt that if anybody establishes himself as the clear leader, the superdelegates would fall in line," said Don Fowler, a former chairman of the Democratic National Committee.

"It is perceived that he is the leader," said Fowler, a superdelegate from South Carolina who supports Clinton. "The trickle is going to become an avalanche."

Superdelegates are the party and elected officials who will automatically attend the Democratic national convention this August in Denver. They can support whomever they choose, regardless of what happens in the primaries.

They are key because neither Obama nor Clinton can win the nomination without them.

Nearly 800 superdelegates will attend the convention. Obama has endorsements from 275, according to the latest tally by The Associated Press. Clinton has 271.5.

Many of the superdelegates who endorsed Obama in the past week said it is time for the party to unite behind him. Obama is coming off a big win in North Carolina's Democratic primary Tuesday. Clinton narrowly won the primary Indiana's primary the same day, but Obama did better than many expected.