Clinton, the senator from New York, won primaries in Rhode Island, Texas and Ohio Tuesday, with Obama only taking Vermont -- his 12th straight win. Pundits had said losses in Ohio and Texas would have meant an end to the viability of Clinton's campaign.
Some observers said Wednesday the Democratic race now hinges on Pennsylvania, which holds its primary April 22.
"The campaigns of both Senator Barack Obama and Senator Hillary Clinton wake up this morning to a seven-week stretch that includes just three contests, and climaxes on April 22 in Harrisburg," The Politico reported.
NBC's Tim Russert, meanwhile, said Wednesday he sees the Democratic race going beyond Pennsylvania.
"This is going to go on until Puerto Rico, June 7," he was quoted by Politico as saying.