And Mr. Penn, asked about the extent to which the campaign might move to draw tough contrasts in the weeks ahead, responded with an e-mail message that suggested Mrs. Clinton did not intend to roll out any new lines of attack now.

“It is really up to the press to dig deeper and vet him now,” he wrote. “That’s not our job.”

Mrs. Clinton woke up Wednesday to the realization that she had lost nearly every advantage she once could claim over Mr. Obama: money, momentum, a lead in national polls and an edge in delegates. Polls suggest that Democrats now view Mr. Obama as more electable than Mrs. Clinton. After her ninth and 10th defeats in a row on Tuesday in Wisconsin and Hawaii, Mrs. Clinton is running out of time.

Her advisers said they still see a road to victory, but acknowledged that it was narrowing. Her goal now, they said, is to do well enough in the remaining states, particularly Ohio, Texas and Pennsylvania, to close Mr. Obama’s lead among elected delegates as the contest moves beyond the primaries and caucuses and into the hands of elected officials and party leaders who serve as so-called superdelegates.

She is pressing challenges to Mr. Obama’s qualifications as a candidate and as a president, and to a certain extent playing for time, hoping that some unexpected event will alter the dynamics of the race in her favor.

There are no large differences between Mrs. Clinton and Mr. Obama on big issues, leaving her struggling to try to gain ground by such means as criticizing him for not agreeing to enough debates. And Mr. Obama himself has been a tricky target for the Clinton campaign; Mrs. Clinton’s associates said that with him seeking to become the first African-American president, race has loomed over their prolonged and sometimes tortured debates about how to discredit him.

Image With the Texas primary approaching, Senator Barack Obamas rally Wednesday in Dallas. Credit... Larry W. Smith/European Pressphoto Agency

The deployment of Bill Clinton to raise questions about Mr. Obama’s qualifications opened Mrs. Clinton to attacks of running a racially tinged campaign. That was particularly unwelcome considering the extent to which this campaign had looked to Mr. Clinton to keep Mrs. Clinton competitive among African-American voters.