It is a question that has hovered over Senator Barack Obama even as he has passed milestone after milestone in his race for the White House: Why is he not doing better?

It shadowed him as he struggled against Senator Hillary Rodham Clinton in many states through the primaries, results that sometimes stood at odds with the huge, enthusiastic crowds that turned out to see him. It was there in the exit polls that suggested that many Democrats were uncomfortable with Mr. Obama, putting an asterisk next to some of his biggest primary victories.

And it is back again as he returns from an overseas trip that even Republicans have described as politically triumphant. In this case, the question is why — given how sour Americans feel about President Bush and the Republican party, and the perception that Mr. Obama is running a better campaign than Senator John McCain — the senator from Illinois is not scoring even higher in national opinion polls.

“They’ve known John McCain for years,” Bill McInturff, a pollster for Mr. McCain, said of survey participants. “But people say in focus groups, ‘Who the heck is Barack Obama? Had you heard of him before six months ago?’ And he’s 46 years old. He’s somebody nobody knows about.”

Peter Hart, a Democratic pollster, said the statistics are a reminder of the particular obstacles that Mr. Obama faces. “Here’s a 46-year-old African American with a narrative that is very unusual and that few other Americans can relate to,” he said. “Add to that the fact that he has had four years in the United States Senate and very little international experience. That’s a large leap for the American public to make.”

Some analysts said that Mr. Obama could be like Ronald Reagan in 1980. Mr. Reagan was up against an unpopular incumbent, President Jimmy Carter, who for all his weaknesses was a known quantity. Only after Mr. Reagan persuaded voters that he was credible as a president did the polls break in his direction.

“It took a long while for the American public to test and look at Ronald Reagan before they were willing to go with him,” Mr. Hart said. “And then, when the dam broke open, it broke open very, very wide.”

Even Mr. Obama’s advisers say they are uneasy about his difficulty so far in breaking the 50 percent barrier — a reminder, in poll after poll, that there many Americans who are not yet ready to cast their lot with him, and may never be.

New York Times