Clinton urges supporters to ignore dire predictions

Clinton spent some of Thursday in West Virginia -the next battleground and where she is favored to win -telling supporters that 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," said Clinton, who would be the nation's first female president. "I think we ought to keep this going so the people of West Virginia's voices are heard."

But, smarting from a crushing loss in North Carolina and a narrower-than-expected win in Indiana on Tuesday, the former first lady also sought to stave off further defections among longtime supporters who saw the pace of the race turn decisively in Obama's favor.

Obama, on the cusp of making history with his bid to be the country's first black president, made an impromptu appearance in the U.S. House of Representatives on Thursday.

It marked his latest effort to woo Congressional superdelegates since Tuesday's contests, which positioned him within striking distance of the party's White House nod in a race that has polarized Democratic voters and raised concerns about unity before the November presidential election.

The latest contests leave Obama with 1,849.5 delegates to Clinton's 1,697, with 2,025 needed to win the nomination. With just six contests remaining and 217 elected delegates at stake, it is mathematically impossible for either candidate to secure the necessary number. This makes the support of the roughly 800 superdelegates -party officials and lawmakers free vote as they chose -vital.

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, whose historic and protracted race with Clinton has riveted and frustrated Americans, 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."