As John McCain, the presumptive Republican presidential nominee, visited Iraq, strategists for Democratic hopefuls Barack Obama and Hillary Rodham Clinton exchanged calculated barbs over accountability, ethics and personal attacks.

Obama communications director Robert Gibbs called on Clinton on Sunday to release full post-White House tax returns; disclose all congressional “earmarks,” or pet projects she had inserted into spending bills; and to release all documents pertaining to activities of the Clinton Foundation and Clinton Library, including a list of donors.

“What is lurking in those documents?” Gibbs asked as the two campaigns had dueling phone conference calls with reporters. “There are gaps that need to be filled,” said senior Obama strategist David Axelrod.

Senior Clinton strategist Mark Penn countered, suggesting the Obama campaign was trying to “deflect public opinion from their losses in Ohio and Texas” and faced overwhelming Clinton strength in Pennsylvania.

“This is a tried and true technique of the Obama campaign that has repeatedly shifted negative when they find the momentum working against them,” Penn said.

While the Democratic camps sparred, McCain, who has linked his presidential hopes to US success in Iraq, was in Baghdad for meetings with Iraqi and US diplomatic and military officials, a US government official said.

McCain was to meet with Gen David Petraeus, the top US commander in Iraq. It also was thought he would meet with Iraqi Prime Minister Nouri al-Maliki.

Closer to home, Obama was heading for Pennsylvania campaign today, with stops later in the week likely in North Carolina and Oregon. Clinton prepared to give a speech on the Iraq war in Washington on Monday.