FACTBOX - Scenarios in U.S. political race

(Reuters) - Barack Obama edged closer to securing his party's nomination while Hillary Clinton vowed to stay in the fight after split victories in primaries in Indiana and North Carolina, the latest battlegrounds in their hard-fought duel for the Democratic presidential nomination.

Republican candidate John McCain has already clinched his party's presidential nomination for the November election.

Here are some scenarios for the presidential nomination battle:

DEMOCRATS

Pressure may grow on Clinton to make a graceful exit from the race. Clinton's slim victory in Indiana may be enough to allow her to continue the battle through the next round of primaries, but Tuesday's results and the math make it difficult for her to win the nomination.

West Virginia holds a primary next Tuesday. Kentucky and Oregon vote a week later and Puerto Rico has one set for June 1, followed by Montana and South Dakota on June 3. The New York senator is favoured in Kentucky, West Virginia and Puerto Rico, while Obama is favoured in Oregon, Montana and South Dakota.

But Clinton's campaign is short of money. She advanced a $6.4 million loan out of her own pocket to keep her struggling campaign alive.

She had hoped a sweep of Tuesday's two contests would allow her to sow doubt about Obama's electability and persuade some superdelegates -- party insiders who are free to back any candidate at the nominating convention -- to move toward her.

Instead Obama, an Illinois senator, won handily in North Carolina and narrowly lost Indiana, lengthening his lead over Clinton in pledged delegates to the August nominating convention and in popular votes won during the four-month primary battle.