Democratic presidential contender Barack Obama picked up a potentially helpful endorsement Friday, even as the national party chairman urged Obama and rival Hillary Clinton to tone down their personal attacks.  VOA National correspondent Jim Malone has the latest on the U.S. presidential race from Washington. 

Democratic presidential hopeful Barack Obama, left, laughs with Senator Bob Casey at the Soldiers and Sailors Museum and Memorial in Pittsburgh, Pa., 28 Mar 2008

Obama won the support of Senator Bob Casey of Pennsylvania.  Casey is a centrist Democrat who is popular in his home state and might help Obama in Pennsylvania's presidential primary on April 22.

Casey told supporters at an Obama rally in Pittsburgh that Obama would set the country on the right path if he is elected president in November.

"A path first of all of change, a path of a new kind of politics, and finally a path of hope and healing," he said.  "I believe in my heart that there is one person who is uniquely qualified to lead us in that new direction, and that is Barack Obama!"

Public opinion polls continue to show Hillary Clinton in the lead in Pennsylvania.  Clinton is counting on a big win in Pennsylvania to keep alive her hopes of winning the Democratic Party nomination.

The lengthy and increasingly bitter nomination fight has some Democrats worried that the party may have trouble unifying behind a candidate in time for the November election.

National Democratic Party Chairman Howard Dean urged both candidates and their supporters to tone down the personal attacks that have intensified in recent weeks.

"We do need to keep in mind that personal attacks now often do have the seeds of demoralization later on, so I want to make sure this campaign stays on the high ground," he said, speaking on CBS television.

Recent polls suggest a sizable number of Democrats might be open to supporting Republican John McCain, depending on who emerges as the Democratic nominee.

Both Obama and Clinton have acknowledged the concerns about party unity in some recent campaign appearances.

"The truth is, I think, that this has been a great campaign, a great primary season," said Obama, speaking in Pennsylvania.  "It has been hard, it has been tough, but it has been hard and tough because both Senator Clinton and I understand what is at stake, how important this race is, how important the next presidency will be to the American people and to families right here in Pennsylvania."

Democratic presidential hopeful, Hillary Rodham Clinton speaks about the economy at Wake Technical Community College in Raleigh, NC, 27 Mar 2008

Clinton also tried to ease concerns during a rally in North Carolina. "When this contest is over and we have a nominee, we are going to close ranks," she said.  "We are going to be united, and I have no doubt about that.  Because the most important goal is for us to put a Democrat back into the White House next January!"

At least one prominent Democrat is suggesting that the time to close ranks is already at hand.  Senator Patrick Leahy of Vermont told public radio in Vermont Friday that there is no way for Clinton to catch Obama in the delegate count and that she should step aside and support Obama.  Leahy previously announced his support for Obama.

Clinton has said she believes the voters should have a say in the 10 remaining nominating contests that last into early June.

Meanwhile, the presumed Republican nominee, Senator John McCain, continues to be overshadowed by the Democratic race.  But McCain is about to embark on a campaign tour aimed at reintroducing him to the public and emphasizing his long experience in foreign policy and national security issues.

The McCain campaign is also releasing the first television ad of the general election campaign recalling the Arizona Republican's courage as a prisoner of war in North Vietnam for five and one-half years.

McCain is also focused on fundraising for the upcoming general election campaign and has slowly begun the closely guarded process of choosing a vice presidential running mate.