(dpa) - Hillary Clinton won Ohio in the Democratic race for the presidential nomination, ending rival Barack Obama's 11-state string of victories, while John McCain captured the Republican nomination with wins in all four states voting on Tuesday.
Clinton, 60, held a commanding lead over Obama of 56 per cent to 42 per cent in Ohio with more than 80 per cent of the votes counted, while the two remained neck-and-neck in the other key contest in Texas. The two rivals split Tuesday's small-state primaries with Obama winning Vermont and Clinton taking Rhode Island.
"You know what they say - as Ohio goes, so goes the nation. Well, this nation's coming back, and so is this campaign," Clinton told ecstatic supporters in Columbus, Ohio.
"Ohio has written a new chapter in the history of this campaign, and we're just getting started."
The Ohio and Rhode Island victories ended Obama's winning streak in 11 straight state contests, which had established him as the clear Democratic frontrunner, giving him a small but significant lead in the delegate count and building nationwide momentum.
Obama congratulated Clinton on her wins but stressed that his lead in delegates to the Democratic Party's nominating convention in August remained intact.
"No matter what happens tonight, we have nearly the same delegate lead as this morning and we are on the way to winning this nomination," Obama told supporters in San Antonio, Texas.
Going into Tuesday, Clinton's campaign had been running short of money while combatting her rival's growing image of inevitability. Even former president Bill Clinton had said that his wife had to win in Texas and Ohio to keep alive her hopes of becoming the first female president.
Some Democrats, however, have urged Clinton to drop out of the race so that Obama can begin confronting McCain in the presidential election without having to devote time and money to the intra-party duel.
The now-certain Republican nominee McCain, 71, told cheering supporters that the general election "begins tonight," after his last challenger, Mike Huckabee, conceded defeat and promised to help unite the party behind the Arizona senator.
"My friends, now we begin the most important part of our campaign," McCain told cheering supporters at a rally in Dallas, Texas.
McCain effectively sealed the Republican nomination weeks ago and has increasingly refocused his presidential campaign on the November 4 general elections.
On Tuesday, he offered the broad outlines of his future campaign strategy, promising victory in Iraq and chiding Democrats for focussing on the 2003 invasion.
"It is of little use to Americans for their candidates to avoid the many complex challenges of these struggles by re-litigating decisions of the past," McCain said.
"The next president must explain how he or she intends to bring that war to the swiftest possible conclusion without exacerbating a sectarian conflict that could quickly descend into genocide, destabilizing the entire Middle East."
The Clinton and Obama camps have become nastier in recent weeks, exchanging barbs over campaign tactics and highlighting their differences over the North American Free Trade Agreement (NAFTA), enacted during Bill Clinton's administration.
While the trade accord has benefited border states like Texas, it is unpopular in Ohio, which has suffered losses of manufacturing jobs. Both candidates say that NAFTA needs to be revised to protect US workers, and both have proclaimed willingness to pull out of the agreement if it cannot be renegotiated.
Clinton aides have questioned Obama's relationship with a developer in Chicago, Antoin Rezko, now on trial for exploiting political relationships with the current governor of Illinois to obtain kickbacks on state contracts.
Obama charged that Clinton was throwing the "kitchen sink" in an effort to rescue her bid for the White House.
Clinton has touted her experience in the White House and longer tenure than Obama in the Senate to argue that she is better prepared for the presidency, and repeated Tuesday that she will be ready to take the helm on "day one."
Obama's message of change has caught on with voters and propelled him to the front of the race, bucking Clinton from her dominating position early in the campaign.