Seeking to change the subject from her trailing Sen. Barack Obama, D-Ill., in terms of delegates, states won and votes from party-recognized contests, Sen. Hillary Clinton, D-N.Y., has been asking why Obama "can't seal the deal."
And while Democratic leaders seem increasingly inclined to suggest quietly that Clinton will not be the nominee, some are also starting to express concern about Obama's weaknesses among a key Democratic group -- white working-class voters -- and what that might mean in November.
At a Phillips 66 gas station in Indianapolis today, Obama was asked why he keeps losing white working-class voters to Clinton. Obama noted that both Clinton and Sen. John McCain, R-Ariz., continue to paint him as an "elitist."
"It's hard for me to figure that out, given that, you know, I was raised with far fewer advantages than either of my two remaining opponents," Obama said.
Still, he pledged to work harder to remind voters of where he came from. "The dinner table would have been very familiar to anybody here in Indiana -- a lot of pot roast and potatoes and Jell-O molds," he said.
Pennsylvania exit polls showed this week that Clinton carried 54 percent of the voters earning less than $50,000 a year, and 58 percent of Democrats without college degrees.
If Obama becomes the nominee, this weakness could have an impact in November when blue-collar voters are more of a force.
"Primaries tend to attract higher income, educated voters -- general elections, somewhat less so," ABC News' Polling Director Gary Langer said.
There are many reasons for Obama's disconnect with this demographic group. Democrat Joann Bruer, an employee at Sam's Hardware in Brazil, Ind., is the kind of working-class white voter who doesn't believe Obama shares her values.
"There are things I've heard about and I just don't trust, and I've got my second thoughts on him," she said.
There are other reasons for Obama's trouble with the lunch-bucket crowd. Clinton is popular among white women and seniors. Many voters prefer Clinton because of concerns about issues or experience. Some are skeptical that Obama -- from the big city, with a cool, cerebral style -- could understand their values.
Then there's the reason cited by one retired Indiana trucker, Bill Came, who supports Obama.
"Race is kind of -- just kind of quiet and laying out there," he said.
Echoing the results from another industrial state Clinton won -- Ohio -- exit polls from the Keystone state indicated that 13 percent of white Democratic voters said race was an important factor in their decision, and three-quarters of them voted for Clinton. Of those white voters who said race was important, if Obama is the nominee, only 54 percent say they would vote for him. Twenty-seven percent said they'll defect to McCain, a small number but possibly enough to turn a red state, blue.
Some of it is racism but the dynamic also may be more complex.
Ronald Walters, a professor of government and politics at the University of Maryland, said, "Many of these places are hit hard. When they look around for who's the cause of it, a lot of times they scapegoat African Americans or Hispanics or someone else."
Clinton has her trouble spots, too. In some states, white men have been a problem for her, and Obama is far more attractive to independents. General election match-ups with McCain show a tough contest, whether the race is between Obama and McCain or Clinton and McCain. But Obama's going to want to improve his standing with working-class whites in upcoming primaries, if only to show the superdelegates that he can deliver them.
Today, in an interview with Linda Douglass of the National Journal, Obama campaign manager David Plouffe tried to play down any impact Obama's race has on his electability, saying, "the vast, vast majority of voters who would not vote for Barack Obama in November based on race are probably firmly in John McCain's camp already."
Avery Miller and Sunlen Miller contributed to this report