Is Obama ready for the onslaught?

Sen. Barack Obama and his campaign face a scenario that a barrage of ads, phone calls and door knocking could not avert — a protracted, two-front war against Sen. Hillary Rodham Clinton and the presumptive GOP nominee, Sen. John McCain.

Even before the votes were cast in Ohio and Texas, campaign officials were dreading an outcome that would keep Clinton, D-N.Y., in the race at least through the Pennsylvania primary April 22. Those seven weeks will cost Obama at least $10 million, and possibly much more, campaign aides say, as he battles a rejuvenated Clinton who will have every incentive to force him into a major mistake.

Obama aides also expect to take concentrated fire from McCain, R-Ariz., and his Republican allies, who already have begun raising questions about the 46-year-old Illinois Democrat's credibility, authenticity and even his patriotism.

Before his victory in Iowa, doubters questioned whether Obama had the stomach to deliver the blows necessary to wear down Clinton's natural advantages. Now, the question is whether he can take a punch.

Some Obama supporters are increasing pressure on him to shift tactics, frame more sharply his criticism of his opponents and begin inoculating himself from the GOP attacks, but Obama remains reluctant to change the approaches he still believes will secure him the nomination. "I have said consistently that we do things differently," Obama said. "It's worked for us so far. And I'm not going to do things that I'm not comfortable in doing."

To be sure, Obama campaign aides think Tuesday's outcomes should not block his path to the nomination. He will maintain a lead in pledged delegates, and any drop in that delegate lead would likely be recouped in Saturday's Wyoming caucuses and next Tuesday's Mississippi primary.

They stressed that they will not be drawn into a fight for Pennsylvania on Clinton's terms, with an expensive, all-out campaign focused on her. Instead, confident that their delegate lead will stand, their main target will shift to McCain.

But Democratic leaders outside the campaign are worried that a candidate who cruised through his only Senate campaign, in 2004, does not know what is about to hit him. Republicans already are planting the seeds for a negative campaign designed to make one overarching point, said Rep. Artur Davis, D-Ala., an Obama supporter and informal adviser: This man is not who you think he is.

"You have to question whether he is equipped to deal with the complex and serious issues that are facing the nation," said Danny Diaz, the Republican National Committee's communications director, who said Republicans will question whether Obama has "a certain level of experience, a certain understanding of the world, of who these leaders are."

Republicans such as Rep. Jack Kingston of Georgia have used Obama's decision not to wear a U.S. flag on his lapel to question his patriotism. Virtually every day, the Republican Jewish Coalition sends e-mails to Jewish voters questioning Obama's commitment to Israel. And darker e-mail and Internet campaigns continue to suggest that Obama is everything from a Muslim to a terrorist sympathizer.

McCain already has made clear how he will try to brand Obama if they meet in November, drawing on his Senate votes on abortion, taxes and guns as evidence that he is out of the mainstream. "He was judged ... as the most liberal senator in the United States Senate," McCain said last week.

But more broadly, Republicans are poised to offer what they consider a stark contrast between McCain's lifetime of experience — in war, in the Senate, in politics — and a caricature of a young, inexperienced neophyte with little but fancy rhetoric to offer.

That is a line of attack that Clinton has labored to make stick for weeks. But McCain advisers think their candidate will be more effective in convincing the public that Obama is not ready to lead the nation, especially during an economic downturn and while waging two wars overseas.