(CNN) -- Sen. Hillary Clinton is arguing that she is ahead of rival Sen. Barack Obama when it comes to the popular vote.
If Michigan and Florida are counted, Sen. Hillary Clinton is ahead in the popular vote.
"I'm very proud that as of today, I have received more votes by the people who have voted than anyone else," Clinton said Wednesday, one day after her decisive win in Pennsylvania.
Not so fast, says Obama's campaign. Clinton's count includes her wins in Michigan and Florida, but the Democratic presidential candidates agreed not to campaign in those states because they violated party rules by scheduling their contests too early.
Obama didn't even have his name on the Michigan ballot, so he received no votes from that contest.
"We think that, in the end, if we end up having won twice as many states and having the most votes, then we should be the nominee," Obama said.
If Michigan and Florida are counted, Clinton is ahead by 100,000 votes -- 15.1 million to Obama's 15 million. Without those states, Obama has a 500,000 vote lead, 14.4 million to 13.9 million.
Clinton says she has received more votes than any Democratic candidate in history.
"It's a very close race, but if you count, as I count, the 2.3 million people who voted in Michigan and Florida, then we are going to build on that," the New York senator said.
Obama's campaign manager said he doesn't expect the Illinois senator to lose his lead by June 3, the date of the last contest.
But Obama is facing questions about why he can't just bring the race to an end.
"You know the way we're going to close the deal is by winning. And right now we're winning. And what we'll do is keep on campaigning in Indiana and North Carolina and Oregon and these other states," he said. Watch how the candidates are prepping for the next contests »
"And at the conclusion of all these contests, people will go back and take a look and say, 'Who's won?'"
Obama leads Clinton in the overall delegate count, 1,719 to 1,586.
Neither candidate can capture the 2,025 delegates needed to secure the Democratic nomination with wins in the remaining Democratic contests, meaning the party's superdelegates will probably decide who gets the Democratic nomination.
Superdelegates are party leaders and officials who vote at the August convention for the candidate of their choice.
Clinton is hoping the popular vote argument will persuade them to endorse her. Of the superdelegates who have made public their choice, Clinton leads Obama 255-232. Watch a report on the superdelegate struggle »
Democratic National Committee Chairman Howard Dean has called on the superdelegates to make up their minds, but superdelegate Debra Kozikowski said it makes sense for her to wait until the primary process is completed.
"We only have a few short weeks to go, and there's been a lot of talk about which states matter and which states don't. Big states, small states -- all states matter, all contests matter," she said on CNN's "American Morning."
The Democrats next face off on May 6, when North Carolina and Indiana hold their contests.
Obama has a comfortable lead in North Carolina, and it's a tight race in Indiana, according to recent polls.
Clinton on Thursday is focusing on North Carolina, where she'll make stops in Fayetteville and Asheville.
Obama has no public events scheduled Thursday.
As the race for the Democratic nomination drags on, Sen. John McCain, the presumptive Republican nominee, is focusing on the general election.
The Arizona senator said earlier this week he isn't sure if the prolonged Democratic race is benefiting him, but exit polls from Tuesday's contest in Pennsylvania suggest that could be the case.
Only 50 percent of Clinton voters in Pennsylvania said they would support Obama if he is the nominee. Twenty-six percent said they would back McCain over Obama, and 19 percent said they would not vote at all.
Among Obama's Pennsylvania voters, 67 percent said they would support Clinton if she is the party's nominee. Seventeen percent said they would back McCain instead, and 12 percent said they would choose neither.
McCain is spending Thursday touring the 9th ward and attending a town hall meeting in New Orleans, Louisiana, as part of his weeklong tour to reach out to people who typically wouldn't vote Republican. E-mail to a friend
CNN's Bill Schneider contributed to this report.