Barack Obama's sprint to the Democratic nomination received another boost Friday as two more superdelegates pledged their support, including one who dropped his backing for Hillary Rodham Clinton's faltering White House bid.

The two Democrats have been lobbying superdelegates _ who are not bound by state results _ to line up behind them in the final push for the nomination. While Obama has presented himself, albeit subtly, as the inevitable candidate, Clinton's efforts have been to ward off further defections and convince the crucial voting block that her candidacy still retained signs of life.

Obama, a step closer to making history after a strong showing in two state primaries earlier this week, appeared to be more convincing in delivering his message.

On Friday, he picked up two new superdelegates, including one who had previously supported the former first lady, Obama spokesman Dan Pfeiffer said. He had received the backing of two others Thursday, an announcement that came shortly after he made an impromptu, and well-received, appearance in the U.S. House of Representatives.

Clinton, who had also earlier made a similar pitch in Congress, campaigned on friendly turf in West Virginia, where she is expected to win in the next vote Tuesday. She told supporters she had faced similar pressure to withdraw before she went on to win New Hampshire, Ohio, Texas and Pennsylvania's primaries.

"I'm running to be president of all 50 states," Clinton, who would be the nation's first female president, said Thursday. "I think we ought to keep this going so the people of West Virginia's voices are heard."

But that race _ one of six remaining contests _ is unlikely to decide a 16-month nomination battle that has both polarized and riveted Democratic voters. With 217 delegates yet to be awarded, it is mathematically impossible for either candidate to clinch the nomination.

As of late Thursday, Obama has 1,849.5 delegates to Clinton's 1,697, with 2,025 needed to win the nomination.

That means the roughly 800 superdelegates are the ones likely to decide the outcome. Of that total, about 260 remain uncommitted. About a third of the undeclared superdelegates are members of Congress.

On the cusp of making history with his bid to be the U.S.'s first black president, he gently nudged Congressional superdelegates for their support.

The first-term Illinois senator was surrounded in the House by well-wishers calling him "Mr. President" and reaching out to pat him on the back. The glad-handers included a few Republicans, as well as Clinton supporters.

But the 46-year-old was quick to note that he faced a formidable adversary.

"Our goal is going to be to try to be to bring the party together as soon as possible," Obama said after his visit. "But we still have contests remaining, and so in no way am I taking this for granted. We're going to have to keep on working."

"My main message is that whichever way you want to go, the sooner that superdelegates make their decision the sooner we will have a sense of who the nominee will be and sooner we can focus on John McCain," Obama told the Fox News Channel outside his Senate office.

Pfeiffer, Obama's spokesman, said candidate plans to receive the endorsement of Rep. Peter DeFazio of Oregon an event Friday in his homestate. Oregon holds its primary on May 20. Continued...