According to the poll, 51 percent of Democratic voters said they expected Obama to win the nomination, down from 69 percent a month ago, while 48 percent saw him as the candidate with the best chance of beating McCain, the presumptive Republican nominee, down from 56 percent a month ago.
Obama's wife sought to put the issue to rest, declining to respond directly to questions about Wright in an interview with NBC's "Today" show recorded for broadcast on Thursday.
"I think we gotta move forward," Michelle Obama said in an excerpt released by NBC News. "You know, this conversation doesn't help my kids. You know, it doesn't help kids out there who are looking for us to make decisions and choices about how we're going to better fund education."
The Illinois senator who could become America's first black president had attended Wright's Chicago church since 1992.
Clinton made a rare appearance on Fox News Channel's "The O'Reilly Factor" and was asked by conservative host Bill O'Reilly whether she felt sorry for Obama in a taped interview.
"Well, I think that he made his views clear finally, that he disagreed, and I think that's what he had to do," she said, calling Wright's comments "offensive and outrageous".
"And people have to, you know, decide what they believe. And I sure don't believe the United States Government was behind Aids," the New York senator said.
Obama defended his opposition to a temporary suspension of the gasoline tax.
"Here's the truth. It would save the average family 30 bucks over the course of three months - $28. Or more precisely 30 cents a day, which is less than you can buy a cup of coffee for at the 7-Eleven," Obama said.
Suspending the gasoline tax would divert money from the federal highway fund, which the tax finances, and cause job losses in construction, Obama said.
McCain told reporters on his campaign bus that Americans deserved a break from the gasoline tax.
"It's a nice little break for Americans, particularly lower-income Americans who generally speaking drive further and drive older cars, which then increases their costs at the gas pump," the Arizona senator told reporters in Allentown, Pennsylvania.
Clinton went on a 45-minute morning commute in a pickup truck with Jason Wilfing, 33, of Plymouth, Indiana. When the pair stopped at a filling station en route to his sheet metal factory job, Clinton paid nearly $64 to fill up half the truck's fuel tank.
