Senator Barack Obama got a major boost Tuesday with victories in the Democratic presidential primaries in Maryland, Virginia and the District of Columbia. Obama remains in a tight race with Senator Hillary Clinton, but the Illinois senator is favored to add to his delegate lead in next Tuesday's contests in Wisconsin and Hawaii. VOA National correspondent Jim Malone reports from Washington.

Sen. Barack Obama makes remarks during a town hall meeting in Waukesha, Wisconsin, 13 Feb 2008

Experts were struck by the margins of the Obama victories on Tuesday, especially in Virginia and Maryland where he won 64 percent and 62 percent of the vote respectively.

Obama benefited from strong support from African-Americans and a burning desire for change among many voters like this man in the nation's capital.

"I just want to see change in the world and I think this primary can bring about change, specifically on Iraq and health care," he said.

Obama has now won eight contests in a row against Clinton and hopes to build unstoppable momentum with victories in next Tuesday's primary in Wisconsin and a Democratic caucus in Hawaii.

"It is about whether we are looking backwards or whether we are marching forward," said Obama. "And when I am the Democratic nominee for president, that will be the choice we have in November."

Political analysts say Clinton must stop his momentum on March 4 when Texas and Ohio hold primaries. Clinton has done better in the large states than Obama, benefiting from better organization and greater name recognition.

Sen. Hillary Rodham Clinton waves to supporters upon her arrival for a campaign stop in McAllen, Texas, 13 Feb 2008

As she campaigns in Texas, Clinton will continue to emphasize her experience to counter Obama's call for change.

"I am a problem solver," she said. "I believe that we need a president, starting on day one, who is going to roll up his or her sleeves and get to work!"

Obama may be gaining an edge because more voters seem to be responding to his message of change.

Anthony Salvanto directs polling for CBS News and noted the results in Maryland, Virginia and Washington, D.C.

"By a large margin, Democratic voters said they were looking for a candidate who could bring change over a candidate with experience," said Salvanto. "Barack Obama handily won those voters looking for change."

Obama's challenge now is to win over more women, Hispanic and working class voters in large states with upcoming races like Ohio, Texas and Pennsylvania.

Democratic Party rules governing the allocation of delegates will make it difficult for either candidate to run away with the nomination anytime soon.

Democrats use a method of proportional allocation that allows the loser in a given primary or caucus to still win a share of the delegates. Republicans generally apply a winner-take-all approach to their contests.

Longtime political observer Tom DeFrank of the New York Daily News predicts the hard-fought Obama-Clinton battle will go on for sometime.

"The bottom line is, the Democratic race is going to continue in a real slugfest, these two titans, well-funded, with fierce support, slugging away at each other for weeks to come," said DeFrank.

The latest delegate estimates give Obama a modest lead. Both candidates have won roughly 1,200 delegates. The first candidate to win 2,025 delegates wins the Democratic nomination.

John McCain, center, flanked by House Minority Leader John Boehner of Ohio, (l), and Rep. Cantor, during a news conference at the Capitol Hill Club in Washington, DC, 13 Feb 2008

In the Republican race, Senator John McCain moved closer to his party's nomination with a sweep of the primaries in Maryland, Virginia and Washington, D.C.

McCain's remaining major challenger, former Arkansas governor Mike Huckabee, continues to draw support from conservatives disenchanted with McCain. But experts say it is virtually impossible for Huckabee to win enough remaining delegates to overtake McCain.

The latest estimates give McCain about 800 delegates, and it takes 1,191 to secure the Republican nomination.