Jae C. Hong, Associated Press
Sen. Barack Obama appears to gather his thoughts before making a call to backers in Charlotte after his plane had mechanical problems.

DENVER — Barack Obama and John McCain agree on this much: The economy is staggering under the Bush administration, and Americans are hurting. But who's to blame and how best to fix it?

Well, they part ways on that, as they made clear in dueling economic speeches Monday on the issue that has taken center stage in their presidential contest.

McCain has been forced into a more defensive crouch because his party has held the White House while jobs, home values, stock prices and consumer confidence have tumbled.

While calling Obama's plans expensive and unwise on Monday, he tried to distance himself from President Bush where he could.

"This Congress and this administration have failed to meet their responsibilities to manage the government," McCain said in Denver. "Government has grown by 60 percent in the last eight years. That is simply inexcusable."

Grounded by plane trouble in St. Louis, Obama phoned his remarks to a gathering in Charlotte, N.C.

Obama's plane made a precautionary landing in St. Louis after the crew had a problem keeping the nose up on takeoff from Chicago.

The plane, an MD-80 Midwest charter, struggled to keep the nose at the necessary angle, as it left for Charlotte, N.C., the pilot said. Later, Midwest Airlines said the problem developed because an emergency slide located in the tail cone of the plane deployed in flight and never threatened the safety of the flight. The National Transportation Safety Board said it planned to investigate the incident.

Federal Aviation Administration spokeswoman Laura Brown said the plane did not declare an emergency but "requested a diversion for mechanical issues they called a flight control problem."

In other developments:

• An Associated Press-Yahoo News poll released Monday asked people to blurt out their first words about the two presidential candidates and one in five say "change" or "outsider" for Obama and "old" for McCain. Those are not only the top responses for each man but the answers that have grown the most since January, when fewer than one in 10 volunteered those descriptions.

Four months from Election Day, the survey underscores that people see quality and question marks in both contenders as they struggle to control their images. Lack of experience is the next most frequently offered view of Obama, 46, the Democrat who came to the Senate from Illinois less than four years ago; for McCain, 71, the Republican senator from Arizona and Vietnam prisoner of war, it's his military service.

Obama is seen as warmer and more empathetic, McCain stronger and tougher. When people are asked whether specific words and phrases apply to each man, the Democrat does 12 percentage points better for caring about "people like you" and is 11 points more likable. McCain has a 24-point edge as a military leader and is 9 points more decisive.

• In a break with tradition, Obama will accept the Democratic presidential nomination in Denver at Invesco Field at Mile High, a 76,000-seat stadium, rather than at the site of the party's national convention across town.

Democratic Party Chairman Howard Dean acknowledged the decision to move Obama's speech on the final night of the Aug. 24-28 convention to the giant open-air football field of the Denver Broncos would raise security challenges but said he and Denver Mayor John Hickenlooper had agreed such concerns won't deter the change in venue.

Dean, in a conference call with reporters, also batted away questions about logistical challenges and added costs the change would produce, saying those things would be worked out in the coming weeks.

Obama, speaking to reporters in St. Louis, said he was excited about the move.

"Sometimes our conventions don't feel like they are open to everybody," Obama said. "For us to be able to do it in Invesco Field is an opportunity for 80,000 people who might otherwise not have been able to participate to get involved."

• Sen. Jim Webb has removed himself from consideration as a running mate to Obama.

In a statement Monday, the Virginia Democrat said he has told Obama that he wants to remain in the Senate, where he believes he is best equipped to serve the people.

Political analysts had said Webb's military and foreign policy credentials could balance out a Democratic presidential ticket that might be deemed soft on national defense. Webb is a decorated Marine veteran of some of the deadliest battles of the Vietnam War.

In 2006, Webb upset Republican Sen. George Allen, won a prized seat on the Senate Armed Services Committee and has become a leading Democratic voice in the Iraq war debate.