The trump card Senator Hillary Rodham Clinton held in her faltering bid for president — her support among the superdelegates who can control the fate of the Democratic nomination — began slipping from her grasp on Friday as Senator Barack Obama moved into the lead on this front, with uncommitted delegates declaring their allegiance to him as others deserted her.
Mrs. Clinton publicly vowed to fight on for the nomination while campaigning on Friday in Oregon. But a new, more conciliatory tone crept into her stump speeches, as she shied away from the more spirited attacks on Mr. Obama that characterized her recent primary battles, instead engaging him more gently on the issues while aiming her fire on Senator John McCain of Arizona, the presumptive Republican nominee.
The superdelegate movement toward Mr. Obama, of Illinois — giving him a net gain of six on Friday alone, with more expected — increased the pressure on Mrs. Clinton, of New York, to at least refrain from divisive remarks, particularly after her comments on Wednesday that lower-income white voters would not support Mr. Obama if he became the Democratic nominee. Aides now say she regrets the comments.
Democratic officials said what had been a trickle of superdelegates declaring for Mr. Obama was turning into a steady stream in the wake of Tuesday’s primaries, when Mrs. Clinton lost by 14 percentage points in North Carolina and narrowly won Indiana. Mr. Obama is just 166 delegates away from the 2,025 delegates needed to secure the nomination.
“I think the tipping point was reached around midnight last Tuesday,” said Representative James E. Clyburn of South Carolina, predicting a “significant and steady movement toward Obama” by superdelegates.
Clinton advisers say attacks on Mr. Obama are no longer enough to change the momentum or the outcome of the nomination race. So continuing to attack him on the campaign trail, at this point, would probably inflict more long-term harm on Mrs. Clinton than on Mr. Obama, her advisers said.
Mr. Obama made his own peace offering to the Clinton camp, albeit a tactical one, suggesting he would be open to helping her retire her campaign debt. “I’d want to have a broad-ranging discussion with Senator Clinton about how I could make her feel good about the process and have her on the team moving forward,” he said. “But as I said, it’s premature right now. She’s still actively running, and we’ve still got business to do right here in Oregon and in other states.”
The tonal change in Mrs. Clinton’s campaigning away from sharp engagement with Mr. Obama could reflect cold political calculation: with elements of the party now coalescing around him, her own political legacy may be at stake in the few weeks remaining before primary voting comes to a close on June 3.
“What Hillary does in the next month is important,” said Representative Rahm Emanuel of Illinois, a House leader who has remained studiously neutral so far, in an interview on Friday at a New Yorker magazine event. “If she spends her time contrasting with Senator McCain, drawing distinctions that help the Democratic Party, that’s productive. If it’s done in another way, that’s not productive.”
Mr. Emanuel declared Mr. Obama the party’s “presumptive nominee,” but his aides emphasized he was merely saying the senator was the front-runner.
The pressure to resolve the nominating fight also heightened speculation about a Clinton-Obama ticket. Although Mrs. Clinton and Mr. Obama refuse to talk about such a possibility, it is increasingly in the interest of each candidate to avoid savaging the other on the chance they could run together.
Mr. Obama, asked at a meeting with voters in Beaverton, Ore., about the possibility of offering Mrs. Clinton the vice-presidential slot, said: “I have not won this nomination yet. I think it would be presumptuous of me to suggest that she’s going to be my running mate when we’re still actively running.”
Senator Edward M. Kennedy of Massachusetts, one of Mr. Obama’s most prominent supporters, dismissed talk of a ticket. “I don’t think it’s possible,” he told Al Hunt of Bloomberg Television.
At a children’s hospital in Portland on Friday, Mrs. Clinton did not refer to Mr. Obama by name but drew a sharp contrast between her plan for universal health care and Mr. Obama’s less inclusive plan: “How can anyone run for Democratic nominee for president and not have a universal health care plan? This is a huge, huge difference and one I feel passionately about.”
But it was nothing Mr. Obama had not heard before and was relatively gentle, at least in comparison with her pointed attacks on the stump and on the airwaves in the most recent primaries, in Pennsylvania, North Carolina and Indiana, where she taunted her rival about his former pastor, the Rev. Jeremiah A. Wright Jr., and Mr. Obama’s remarks about “bitter” small-town voters.
Bill Carrick, a longtime Democratic campaign consultant who is neutral but who has close ties to many in the Clinton inner circle, said, “She’s very, very sensitive to the position she’s in now.” He added: “Definitely as she campaigns in these upcoming states she will stress her commitment to the Democratic Party and the stakes in the fall. She’s clearly sending a message to those voters that it’s in their interest to support the party in the fall, whoever the nominee is.”
Publicly, Mrs. Clinton is signaling that she is in the fight to win. In her speeches and in personal pleas to undecided superdelegates, she argues that she has proved better than Mr. Obama at attracting support from Latinos, Roman Catholics and older and working-class voters, and is better equipped than he is to win the swing states in November.
“There is no margin for error,” she said on Thursday night at a fairground in Central Point, Ore. “We need to elect someone who understands how Washington works and is ready from Day 1.”
The Clinton campaign began running new television advertisements in West Virginia and Oregon that do not mention Mr. Obama. The West Virginia spot focuses on trade deals and special interests, while the Oregon one criticizes the Bush administration’s conduct of the Iraq war.
On Thursday, Mrs. Clinton affirmed her intent to fight for victories in the six Democratic primaries left. She tells her audiences, and herself, that the exercise strengthens party muscles.
“The more we compete in Democratic primaries,” she said at a rally at a Sioux Falls, S.D., airport hangar, “the stronger the Democratic Party will be.”