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State Condoleezza Rice might be his running mate was widely seen as an effort to shift the campaign focus from his business and tax record.

But the overall impression left by the race so far is one that is as static as it is angry. Polling experts point to several reasons for the at least temporary stability, while noting that the early jousting is giving the relatively small pool of undecided voters information that they may take some time to fully consider. Both the NBC/WSJ poll and a recent CBS/New York Times survey did find that both candidates had seen an erosion in their approval ratings in recent weeks.

Looking back to 2004, the last time an incumbent president was on the ballot, Charles Franklin, who directs the Marquette Law School's poll, noted that then-President George W. Bush had an approval rating of roughly 46 percent at the time that Sen. John Kerry of Massachusetts wrapped up the Democratic nomination. By Election Day, that figure had crept up to 52 percent.

"That's pretty modest movement on a month-to-month basis; it puts the stability we're seeing this time into some perspective," he said.

But one key difference between the two cycles is the deepening partisan chasm in American politics

"The other thing I would point to is just how extraordinarily polarized the parties and the electorate have become over the course of the health care debate and the 2010 election," Mr. Franklin said.

He noted that while the persistent weakness of the economy would normally be a recipe for defeat for any incumbent, polls show that many undecided voters remain ambiguous on the question of who is to blame.

"The low marks on the economy would normally make you think, 'How can this guy be re-elected? ' ... but polling shows a lot of people pointing to [Mr. Bush] and Wall Street."

Terry Madonna, the political scientist who directs polling at Franklin & Marshall College, said the persistence of Mr. Obama's lead defied historic trends on economics and presidential popularity.

"This is an election that Obama should lose by any historic measure," he said. "Unemployment in 1980 and '92 [both years when incumbent presidents were defeated] was worse ... but Romney has yet to convince people he's an acceptable alternative. And right now, the president's campaign is doing a better job defining [Mr. Romney] as this rich guy who sent jobs overseas."

But the fact that he is still being defined in many voters' minds represents an opportunity as well as a danger to the challenger. Voters have had years to observe and make up their minds on Mr. Obama, making his image less malleable under the ads and arguments of the Romney campaign. For many voters, Mr. Romney's public portrait has yet to come into similarly sharp focus.

"The narrative hasn't settled in," Mr. Coker said. "The conventions will give Romney at least a chance to create an image different from the one Obama has been able to stick on him. ... If that campaign can make him a little bit more of a regular guy, I think a lot of that undecided vote could flow to Romney."

Mr. Coker said that at a similar point in the summer of 1980, President Jimmy Carter held and significant lead over challenger Ronald Reagan, only to see Mr. Reagan win in a landslide.

Mr. Romney, heading to his foreign trip this week, will have a chance to burnish his image as a plausible president in a series of meetings with heads of state. But Mr. Franklin is among those who feels his election prospects will be better served by his return to the U.S. and to the economic issue that is the centerpiece of his campaign argument.

"The international stuff is sort of a wild card," he said, "but international crises usually help the incumbent, in the short term although not necessarily in the long term."

He noted that while the Iraq War battered Mr. Bush's popularity, he actually enjoyed a boost in polling approval with the beginning of the conflict.