FACTBOX: Scenarios in U.S. political race

(Reuters) - Hillary Clinton's victory in Pennsylvania assured her hard-fought battle with Barack Obama for the Democratic presidential nomination will go on for at least another week.

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

Even with her win in Pennsylvania on April 22, Clinton still trails Obama in delegates to the August nominating convention and in votes won during the four-month primary battle.

The two contenders head to the next major contests on May 6 in Indiana, which has been considered a toss-up, and North Carolina, where Obama has been ahead in state polls.

If Obama wins both, it would likely spark another flood of calls for Clinton to step aside and allow Obama to focus on the race with McCain.

Clinton victories in both states could begin to persuade some superdelegates -- party insiders who are free to back any candidate at the nominating convention -- to move toward her. But independents and Republicans will be able to vote in Indiana's contest, which could give Obama an edge since he has attracted those voters in the past.

After those two states, just six more contests will remain before the Democratic race concludes on June 3. Clinton is favored in Kentucky, West Virginia and Puerto Rico, while Obama is favored in Oregon, Montana and South Dakota.

Neither candidate will win enough delegates in the state contests to clinch the nomination, leaving the decision at that point to the party's nearly 800 superdelegates.

Both Clinton and Obama want to show them they are the candidate with the best chance to beat McCain in November.

Many Democratic strategists expect a wave of superdelegates to move toward the leader after the final contest on June 3, essentially deciding the race before it reaches the August convention in Denver.

REPUBLICANS

John McCain, who has clinched his party's presidential nomination, has begun a national campaign and is trying to set the agenda for a autumn race against either Obama or Clinton.

(Writing by John Whitesides, editing by David Wiessler)

(For more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at http:blogs.reuters.com/trail08/)