Barack Obama collected victories Tuesday in Maryland, Virginia and the District of Columbia, adding momentum to his campaign for the Democratic presidential nomination.
Obama claimed a "new American majority" and began focusing his attention on John McCain, the leading Republican candidate.
"This is what change looks like when it happens from the bottom up," Obama said, speaking Tuesday night to a crowd of about 17,000 at the University of Wisconsin. "This is the new American majority."
A tally by The Associated Press showed Obama with 1,223 delegates, compared to Clinton's 1,198, which puts him in the lead for the first time since the primaries began.
A total of 2,025 delegates are required to secure the nomination.
Obama said McCain -- who is outpacing Mike Huckabee in the Republican race -- had a hand in failed policies brought forward by current president George Bush.
"George Bush won't be on the ballot this November, but the Bush-Cheney war and the Bush-Cheney tax cuts for the wealthy will be on the ballot," Obama said.
Meanwhile Obama's rival for the Democratic nom, Hillary Clinton, looked beyond Tuesday's losses to Texas and Ohio where she hopes to shore up her campaign.
"We're going to sweep across Texas in the next three weeks bringing our message of what we need in America," she told supporters in Bush's home state Tuesday night.
"There's a great saying in Texas, all hat and no cattle. Well, after seven years of George Bush, we need a lot less hat and lot more cattle," she told the El Paso crowd."
Clinton called on supporters to come out in force in Ohio, calling it a key battleground.
"Ohio is really going to count in determining who our Democratic nominee is going to be," Clinton told a Cincinnati radio station before flying into Texas, adding that she is the underdog candidate in the Tuesday primary in Wisconsin.
McCain meanwhile offered a grim warning of the direction Obama or Clinton would take the country.
"They will paint a picture of the world in which America's mistakes are a greater threat to our security than the malevolent intentions of an enemy that despises us and our ideals."
