Mar 5, 2008, 2:42 GMT
Washington - Barack Obama won Vermont while Hillary Clinton captured Rhode Island in the Democratic race for the presidential nomination, and John McCain took Texas to clinch the Republican campaign in voting on Tuesday.
McCain, 71, swept all four states on Tuesday, major television networks projected, and his last challenger, Mike Huckabee, conceded defeat and promised to help unite the Arizona senator.
Obama, 46, and Clinton, 60, split Tuesday's small-state primaries. The campaigns for the hotly contested centre-left Democratic nomination were awaiting results in the big states of Texas and Ohio.
Last month, Obama emerged as the clear Democratic frontrunner. If Clinton loses in both Ohio and Texas, the former first lady would probably fall insurmountably behind.
Pre-election polls in Texas showed a dead heat, and Clinton had held a small lead in Ohio.
Heading into Tuesday's voting, Obama had won 11 consecutive state contests, establishing himself as the frontrunner in the delegate count and building nationwide momentum.
Meanwhile, Clinton's campaign has run short of money and struggled to combat her rival's growing image of inevitability. Her Rhode Island victory broke Obama's four-week winning streak.
Former president Bill Clinton has said that his wife must win in Texas and Ohio to keep alive her hopes of becoming the first female president. Hillary Clinton has vowed to go forward with her campaign regardless of Tuesday's outcome.
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 continue duelling with Clinton.
McCain effectively sealed the Republican nomination weeks ago and has increasingly refocused his presidential campaign on the November general elections. He has begun making the case for keeping US soldiers in Iraq - a position Clinton and Obama oppose.
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.
The Clinton campaign has drawn attention to allegations that one of Obama's economic policy aides met with a Canadian official to calm fears that he would ditch NAFTA, saying Obama's comments were just political rhetoric.
Obama responded by saying that Clinton was pedaling a false story of 'contradictions and winks and nods that has been disputed by all parties involved.' He also pointed out that Clinton and her husband pushed NAFTA through Congress in 1993.
Clinton aides have raised 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 usually says 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.
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