The Democratic contenders on Wednesday both focused their campaigns on Texas, which has emerged as a critical race for the campaign of Senator Hillary Rodham Clinton.
With Senator Barack Obama having won primaries in Wisconsin and Hawaii on Tuesday by broad margins across nearly every voter group, Mrs. Clinton has now lost 10 contests in a row since splitting votes and delegates with him on Super Tuesday, Feb. 5. Mrs. Clinton's aides have calculated that she must win the party's next two major contests, in Texas and Ohio, on March 4.
Senator John McCain, all but assured of the Republican nomination, is in Ohio on Wednesday. Mr. McCain has turned his attention to Mr. Obama, calling on him to pledge to abide by the limits of public financing for the campaign.
Mrs. Clinton also focused on Mr. Obama as she went on the offensive early Wednesday in a speech at Hunter College in Manhattan, arguing that her rival has substituted rhetoric for practical experience.
"It is time to get real," Mrs. Clinton, of New York, said. "To get real about how we actually win this election and get real about the challenges facing America. It's time we moved from good words to good works, from sound bites to sound solutions."
It is a familiar theme, but Mrs. Clinton delivered it with fresh intensity after the crushing defeats in Wisconsin and Hawaii on Tuesday.
Mrs. Clinton spent Wednesday morning in New York raising money before flying to Texas to campaign. Voters in Texas and Ohio, along with Rhode Island and Vermont, go to the polls in less than two weeks in contests that Democratic strategists say Mrs. Clinton must win if she is to have any hope of capturing the nomination.
Mr. Obama sought to counter Mrs. Clinton's charges at a campaign appearance on Wednesday afternoon in Dallas, saying "it is time to move beyond the politics of yesterday."
"Today, Senator Clinton told us that there was a choice in this race and you know, I couldn't agree with her more," Mr. Obama said. "But contrary to what she's been saying, it's not a choice between speeches and solutions, it's a choice between a politics that offers more of the same divisions and distractions that didn't work in South Carolina and didn't work in Wisconsin and will not work in Texas."
"Or a new politics of common sense, of common purpose, of shared sacrifice and shared prosperity," he said. "It's the choice between having a debate with John McCain about who has the most experience in Washington or having a debate about who's most likely to change Washington."
One day after victories in Wisconsin and Hawaii, Mr. Obama drew about 17,000 people to a rally at the Reunion Arena in downtown Dallas. While the primary is on March 4, early voting began on Tuesday and Mr. Obama encouraged his supporters to cast their ballots soon.
"As this movement continues, as this campaign builds strength, there are those who will tell you not to believe," Mr. Obama said. "There are those who will tell you it can't be done."
Saying he offered voters a chance to break from the policies of the past years, including the war in Iraq and the current economic situation, Mr. Obama said the race was a choice "that is not just about turning a page on the politics of the past but of turning the page on the policies of the past."
David Plouffe, the campaign manager for Mr. Obama, said that Mr. Obama had amassed a 159-delegate lead over Mrs. Clinton, based on his campaign tally. Following a win in Wisconsin by 17 percentage points, Mr. Plouffe said Mrs. Clinton would need to win in Texas and Ohio by double-digits to gain an edge in the fight for delegates.
"We have opened up a big and meaningful delegate lead," Mr. Plouffe said, speaking in a conference call with reporters. "They are going to have to win landslides to reverse it."
Reflecting Mr. Obama's lead on the Democratic side, Mr. McCain focused his criticism on him during a news conference in Columbus on Wednesday. He pounded Mr. Obama yet again for his commitment in writing a year ago to accept public funds for the general election about $85 million for each candidate if the Republican nominee did the same. In doing so, Mr. Obama would have to surrender a phenomenal advantage in fund-raising and accept the limits of public financing.
Mr. McCain, who was the only other presidential candidate to sign on to the pledge, was responding to a column by Mr. Obama in USA Today on Wednesday in which the candidate wrote that he remained open to public financing, but that he was concerned about the spending of outside groups on behalf of candidates and that he wanted to reach a "meaningful agreement" with whoever is the Republican nominee. But he did not expect, he wrote, "that a workable, effective agreement will be reached overnight."
As conditions for such an agreement, Mr. Obama wrote that candidates "will have to commit to discouraging cheating by their supporters; to refusing fund-raising help by outside groups; and to limiting their own parties to legal forms of involvement."
Mr. Obama has broken all political fund-raising records in this election he has taken in more than $150 million so far, $36 million in January alone, and Mr. McCain's advisers have privately questioned why he would disarm himself of that advantage and not spend the prodigious amounts he has raised on his own. Mr. McCain, who raised $12 million in January, appears to be preparing for that possibility, but in the meantime is attacking Mr. Obama as someone who could not keep his word and should bear the responsibility for breaking the pledge.
If Mr. Obama or Mrs. Clinton do not accept public financing in the general election, Mr. McCain said, "I obviously would have to re-evaluate."
As the war of words continued throughout the day, Bill Burton, Mr. Obama's national campaign spokesman, e-mailed reporters with the retort that Mr. McCain, who has built a large part of his political persona around limiting the amount of money spent on campaigns, has not accepted public financing for the primaries and caucuses. On that score, neither has Mr. Obama.
Reporting was contributed by John M. Broder in New York, Elisabeth Bumiller in Columbus, Ohio, and Jeff Zeleny in Texas.