Boost for Obama, but bump for party

The surprise endorsement of Sen. Barack Obama by a popular senator in a crucial state on Friday underlined the ferment in the Democratic presidential race and the serious obstacles facing Sen. Hillary Rodham Clinton as she tries to rescue her candidacy.

Compounding the challenge, one of Obama's most prominent supporters, Sen. Patrick J. Leahy of Vermont, said Friday that Clinton should withdraw from the race.

The Clinton campaign showed resolve in the face of the developments, rallying supporters and donors and enlisting prominent surrogates to fight back. Clinton told aides that she would not be "bullied out" of the race, and in a conversation with two Democratic allies, she compared the situation to the "big boys" trying to bully a woman, according to interviews with them.

Clinton said she was in the contest to stay. "I believe that a spirited contest is good for the Democratic Party," she said at a late-afternoon news conference in northwestern Indiana. "We will have a united party behind whoever that nominee is."

The developments, including the endorsement of Obama by Sen. Bob Casey of Pennsylvania, where Clinton is seeking a major primary victory on April 22, occurred as uneasiness grows among Democrats over a race that has become closer, more extended and more bitter than expected.

In interviews, Democratic leaders said they are concerned that the increased tension between the two campaigns is hurting the party's chances of winning the White House in November.

Clinton's aides said they could see no circumstance in which she would withdraw unless she loses Pennsylvania, although two senior advisers and one close ally said they would urge her to quit the race if she loses Indiana on May 6.

"The tone has changed in the last three or four weeks," he said in an interview. "And the emotional content has increased to the point where it is in some cases unhealthy."

"If we have an ugly, divided convention, we will lose," he said.

Dean said he wants the contest settled well before the party's convention at the end of August. He urged so-called superdelegates -- uncommitted party leaders and elected officials -- to unify behind a candidate soon after the last primaries, on June 3.

The next contest is in Pennsylvania, where polls suggest Clinton is in a strong position and her aides are confident of a sizable victory there, even after Obama's endorsement by Casey, an abortion opponent who comes from a prominent Pennsylvania political family and could help Obama with white, more socially conservative Democrats.

Some of Clinton's associates, however, now say Indiana is a must-win state for her: a defeat there would make it even more mathematically improbable that she would win the nomination and undercut any boost she might get out of Pennsylvania.

"There is no way that Senator Clinton is going to win enough delegates to get the nomination -- she ought to withdraw and she ought to be backing Senator Obama," Leahy told Vermont Public Radio.

"I am very concerned," he said. "John McCain, who has been making one gaffe after another, is getting a free ride on it because Senator Obama and Senator Clinton have to fight with each other. I think that her criticism is hurting him more than anything John McCain has said."