(CNN) -- Democrats faced the prospect of at least six more weeks of tough campaigning after Hillary Clinton's Tuesday night wins in Tuesday's primaries in Ohio and Texas as she escaped a knockout blow by Barack Obama.
Hillary Clinton won primaries in Rhode Island, Texas and Ohio Tuesday night while Barack Obama won Vermont.
Both Democratic contenders are eyeing Pennsylvania -- the last heavyweight state on the primary calendar -- as the next major battleground. The state votes April 22, after Democratic caucuses in Wyoming on Saturday and a Mississippi primary March 11.
"Ohio has written a new chapter in the history of this campaign, and we're just getting started," Clinton told supporters in her victory speech in Ohio.
"More and more people have joined this campaign, and millions of Americans haven't spoken yet. In states like Pennsylvania and so many others, people are watching this historic campaign, and they want their turn to help make history."
After winning the biggest prizes in the February 5 Super Tuesday contests, the New York senator and former first lady dropped 11 straight primaries and caucuses to Obama and watched her leads in Ohio and Texas dwindle to single digits in published polls. Watch Clinton address supporters in Ohio »
Obama supporters began calling for her to quit the race in order to head off a more divisive endgame, and even her husband -- former President Bill Clinton -- told supporters she would be unable to win the nomination without victories in those states.
But Clinton hit back with a television ad aimed at raising concerns about Obama's experience, an ad juxtaposing a sleeping child with a late-night emergency call to the White House.
Her campaign also jumped into the controversy over an Obama adviser's meeting with Canadian officials to discuss trade policy as the Illinois senator was calling for changes in the North American Free Trade Agreement, accusing him of telling voters one thing and the largest U.S. trade partner another.
The attacks appeared to hit their mark: About one in three voters in the Texas and Ohio primaries made up their minds in the last week, and those who did broke heavily for Clinton.
"Obama gave his adversaries a big gift when he stumbled and mismanaged this NAFTA issue in a state that's economically pressed," said CNN contributor Paul Begala, a Clinton backer. "Hillary moved ahead on that, and I think that's why we're calling Ohio for her."
Obama advisers point out that they closed the gap drastically in three weeks of intense campaigning, and that despite Tuesday's losses, he will still lead Clinton in the pursuit of the national convention delegates who will choose a nominee in Denver in August. Watch Obama react to primary results »
"The real measurement tonight is not whether or not Hillary Clinton can win Ohio or Texas, it's whether she wins by a large enough margin to win the nomination," Sen. John Kerry, the party's 2004 presidential nominee, told CNN. "And she has to win by a very big number for the math to work over the course of the next week."
Kerry said Clinton's attacks on Obama -- which were accompanied by complaints that the first-term senator was getting kid-glove treatment by reporters -- sounded "sort of desperate" and risked turning off voters in November. But other observers said Obama can't continue to take those kind of hits without responding.
"He must begin to answer some of these charges by Sen. Clinton," said Donna Brazile, a CNN contributor who managed former Vice President Al Gore's 2000 presidential bid. "She's gotten away with four days of Sen. Obama, you know, not being able to get back on offense."
David Gergen -- a former adviser to the Nixon, Reagan and Clinton administrations -- said Obama "has to throw a punch."
"He has to go on the offense," Gergen said. "He's foresworn going after her with negative ads, but he can't be hit around the head and shoulders and not fight back." E-mail to a friend