Democratic presidential contender Barack Obama focused on economic concerns Thursday, and in the process raised what the Democrats feel may be a potent issue, Republican John McCain's wealth.  The back and forth in the U.S. presidential campaign comes amid new public opinion polls showing that McCain has closed the gap with Obama in the race for the White House.  VOA National correspondent Jim Malone has more from Washington.  

Senator Barack Obama speaking at John Tyler Community College in Chester, Virginia, 21 Aug 2008

Senator Obama campaigned in Virginia where he vowed to fight for the economic concerns of middle class families if elected president.

Obama then turned to a comment made by his Republican opponent, Senator John McCain, in an interview with the Politico, a political news publication and website based in Washington.

"Somebody asked John McCain, how many houses do you have?  And he said, I'm not sure," Obama said. "I'll have to check with my staff.  Now think about that.  I guess if you think that being rich means you have to make $5 million, and if you do not know how many houses you have, then it is not surprising that you might think the economy is fundamentally strong."

The McCain campaign responded that Senator McCain and his wife Cindy own at least four homes in three states.  Newsweek magazine recently estimated that Senator McCain and his wife, who comes from a wealthy family, own at least seven properties.  

A McCain statement also noted that Senator Obama earned more than $4 million last year and recently enjoyed a vacation on a private beach in Hawaii.

Senator McCain is taking a few days off from the campaign as the political spotlight shifts to the Democratic National Convention that begins Monday in Denver, Colorado.

McCain will be officially nominated at the Republican convention in Minneapolis-St. Paul, Minnesota, which begins September 1.

Sen. John McCain talks to reporters after touring the Chevron Genesis oil rig platform in the Gulf of Mexico near New Orleans, Louisiana, 19 Aug 2008

In an earlier campaign appearance this week, McCain continued to question Senator Obama's plan to set a timetable for the withdrawal of U.S. troops from Iraq.

"He said I am questioning his patriotism," said McCain. "Let me be very clear.  I am not questioning his patriotism.  I am questioning his judgment.  I am questioning his judgment."

Both candidates are expected to announce vice presidential running mates soon.  Obama is expected to reveal his pick by Saturday, while McCain is likely to wait until after the Democratic convention.

The latest public opinion polls show McCain gaining on Obama.  New surveys from NBC News and the Wall Street Journal plus CBS News and the New York Times both show Obama leading McCain by a margin of three points, 45 to 42 percent.  Obama previously had a six-point lead in both polls.

Democratic pollster Celinda Lake says the McCain campaign has been on the offensive against Obama in recent weeks, and that strategy appears to be paying off.

"Voters think by almost two to one that he has been more negative in his [McCain's] campaigning that Barack Obama," she said. "Having said that, however, we know that in our business, voters always complain about negative campaigning, but it also works.  And so the great irony here is that despite the fact that McCain is seen as overwhelmingly running the more negative campaign, people think that what they have heard about Barack Obama is more negative than what they have heard about John McCain.  And this is an example of a situation where negative does work."

Political experts say Obama has an opportunity to regain the momentum during next week's Democratic Convention.  The four-day convention will feature speeches by Obama's former rival, Senator Hillary Clinton, her husband, former President Bill Clinton, and former Vice President Al Gore.

The convention will draw to a close next Thursday after Obama formally accepts his party's nomination with a speech at a football stadium in Denver in front of 75,000 people and a national television audience.