FACTBOX: Scenarios in political race

(Reuters) - Democrat Barack Obama has easily won three more nominating contests, extending his winning streak over rival Hillary Clinton and building momentum in a hard-fought U.S. presidential race.

Republican presidential candidate John McCain, the all-but-certain nominee of his party after rival Mitt Romney dropped out, defeated former Arkansas Gov. Mike Huckabee in Virginia, Maryland and the District of Columbia.

Here are some scenarios for the presidential nomination battle in the coming weeks:

* Illinois Democratic Sen. Obama, who emerged from the 24-state Super Tuesday battle on February 5 in a virtual draw with New York Sen. Clinton, won weekend elections in Louisiana, Washington, Nebraska, Maine and the Virgin Islands, and extended the hot streak Tuesday in Maryland, Virginia and the District of Columbia.

Obama is poised to do well in next week's battles in Wisconsin and Hawaii as well.

But since Democrats distribute delegates among candidates in proportion to their vote statewide and in individual congressional districts, those who lose a state can still come away with a big chunk of delegates.

By the end of February it is likely neither Clinton nor Obama will emerge with a significant lead in delegates. Clinton is focusing on contests in delegate-rich Texas and Ohio on March 4 as her best chance to gain ground on Obama.

* Clinton, a former first lady, is well known to voters and once had a big lead in national polls, even as Obama won early state contests in Iowa and South Carolina and gained momentum with celebrity endorsements and huge crowds. A longer campaign could benefit Obama as he gets a chance to introduce himself to more voters.

* A close contest could hinge on nearly 800 Democratic "superdelegates" who can support the candidate of their choice. Clinton and Obama are avidly courting those elected officials and party insiders, who account for one-fifth of the party's 4,049 delegates.