In the U.S. presidential race, Democrat Barack Obama continues to build momentum in the party nomination battle with rival Hillary Clinton. On the Republican side, John McCain is hoping some high-profile endorsements will win over some of his stubborn conservative critics. VOA national correspondent Jim Malone is following the 2008 presidential campaign in Washington.

Obama is looking to Tuesday's nominating contests in Wisconsin and Hawaii to extend his primary and caucus winning streak.

Obama has won eight straight contests over Hillary Clinton since February 9, and is favored in both Wisconsin and Hawaii.

Obama got a boost Friday when he won the endorsement of a large labor union, the 1.9 million-member Service Employees International Union.

Both Obama and Clinton are looking ahead to a major showdown on March 4 when Ohio and Texas hold primaries. Both states have large numbers of delegates.

Clinton has been leading in both states and political experts say she needs a good showing in both to slow down Obama's momentum.

As she campaigns in Ohio, Clinton is casting herself as a candidate of action, not words.

"There is a big difference between us, speeches versus solutions, talk versus action," she said. "You know some people may think words are change. But you and I know better. Words are cheap."

Obama says Clinton's escalating attacks are a sign of desperation, and he is turning his attention more and more to the expected Republican presidential nominee, Senator John McCain of Arizona.

"If you want the same as we have had over the last seven years, then I think John McCain is going to be a great choice," he said.

McCain says he looks forward to running against either Clinton or Obama in the general election campaign.

"I have not observed every speech he has given, obviously, but they are singularly lacking in specifics," he said. "And that is when, as the campaign moves forward, we will be portraying very stark differences."

McCain is expected to win the endorsement of former President George Bush in Texas on Monday. On Thursday, McCain was endorsed by former Massachusetts governor Mitt Romney, who dropped out of the race last week.

McCain is well on his way to winning enough delegates to claim the Republican nomination, even though former Arkansas governor Mike Huckabee remains in the race and some conservative Republicans still oppose him.

But the Democratic nomination battle is far from being resolved, and many experts now believe the party's so-called super delegates may play a decisive role down the road.

Super delegates are Democratic Party activists or elected officials who can support any candidate they want regardless of the primary or caucus results in their state. They make up about 800 of the roughly 4,000 Democratic delegates and most of them have not yet committed to either Clinton or Obama.

In recent days, a handful of super delegates have switched their support from Clinton to Obama, including Congressman John Lewis of Georgia, a respected pioneer in the struggle for civil rights.

University of Virginia political analyst Larry Sabato says there is reason for the Clinton campaign to be concerned.

"Something like this could potentially be the opening in the dike that leads to a great gush of water if others follow him," he said.

Many experts believe the Clinton-Obama race will remain unresolved right up until the Democratic national nominating convention in late August in Colorado, raising the possibility that the super delegates could play a deciding role.

Longtime Democratic strategist Tad Devine says that could wind up dividing the Democratic Party.

"It is going to be a potentially divisive and maybe even brutal process," he said.

Most delegate estimates give Obama a modest lead over Clinton at the moment, with both candidates having won roughly 1,200 delegates so far. To win the Democratic nomination, 2,025 are needed.