Since March, she has won around half a million more popular votes than Obama, and she argues that in the general election against Republican John McCain, she is the better bet.
"In the final assessment I ask you to consider these questions. Which candidate best represents the will of the people who voted in this historic election?" the New York senator asked.
About 200 party elders, known as superdelegates, hold the balance of power in the fight for the nomination with votes equal to those of the state delegates.
Obama's aides questioned her popular vote claim.
Her assertion includes estimates for caucuses in Iowa, Nevada, Maine and Washington state, where no official candidate popular vote is available.
It also includes the results from Florida, where no campaigning occurred, as well as Michigan, where Obama did not receive any votes because his name was not on the ballot.
As the latest primary results rolled in, Obama made barely any mention of Clinton, except to predict her loyal support after he becomes the Democratic nominee.
"She is going to be a great asset when we go into November to make sure that we defeat the Republicans. That I can promise you," he said while campaigning in Mitchell, South Dakota.