( dpa ) - While Hillary Clinton is already looking forward to a key round of primaries in Ohio and Texas in early March, Barack Obama is hoping that wins in Wisconsin and Hawaii on Tuesday will give him unstoppable momentum in the Democratic presidential nominating contest.
Obama will have pulled off a string of 10 consecutive state victories over Clinton if he wins Wisconsin and Hawaii Tuesday. Polls in Wisconsin have shown Obama - elected to the Senate from neighbouring state Illinois in 2004 - with a slim lead, while he spent much of his life growing up in Hawaii.
Clinton's campaign has for weeks played down expectations in state contests that came immediately after Super Tuesday, where the two Democrats battled to a draw in more than 20 state electoral contests earlier this month. The New York senator has staked her hopes of winning the nomination on Texas and Ohio on March 4.
Clinton has characterized herself as a woman with solutions for the country, in contrast to the lofty rhetoric that has turned Obama into the favourite.
"You can choose speeches, or solutions. You can choose talk, or action," she said at a rally in Ohio.
Obama fired back in Wisconsin, accusing Clinton of putting up "boxing gloves" against the Republicans instead of working together with the opposition to hammer out solutions for the country.
Obama handily won the so-called Potomac primaries of Virginia, Maryland and Washington DC last week and - for the first time since the very first contest in Iowa - pulled ahead of Clinton in the battle for delegates to the Democratic Party's nominating convention in August.
He has gained added momentum from the backing of a key national labour group, the Service Employees International Union, which has 1.9 million members, and another large union, the United Food and Commercial Workers.
On the Republican side, Senator John McCain, 71, heads into Tuesday's contests virtually guaranteed of winning his party's nomination.
On Monday, he got the endorsement of former president George HW Bush - father of the current US president - who called him the best person to lead the United States at a critical time of war.
Last week, the Arizona senator picked up the endorsement of his former rival Mitt Romney, who urged all of the delegates he had won to back McCain at the Republican Party's own nominating convention in September.
Romney's move all-but doomed the chances of former Arkansas governor Mike Huckabee, whose only real hope of capturing the nomination was to prevent McCain from taking all 1,191 delegates needed to win outright - and hope that Romney's delegates would back him instead of McCain at the convention.
McCain has spent recent days drawing contrasts with his possible Democratic opponents and urging Republicans to unite behind him ahead of general elections on November 4.