Sept. 6 (Bloomberg) -- Another top aide resigned from Republican Fred Thompson's campaign as the former Tennessee senator made his bid for the White House official.

The latest staff member to depart is Mark Corallo, a senior strategist and spokesman who was one of the first people to join Thompson's campaign. Corallo resigned yesterday, hours before Thompson formally declared his candidacy in a video posted on his Web site just after midnight, a campaign official said.

Corallo's resignation follows the departure of at least three other members of Thompson's communications staff, acting campaign manager Tom Collamore and several other aides in recent months. Thompson last month brought in Bill Lacy, a White House political director under President Ronald Reagan, to run the campaign, causing friction among some of the earlier hires.

``There appears to be something dysfunctional inside the Thompson campaign,'' said Barry Burden, a political science professor at the University of Wisconsin in Madison. ``He has been hemorrhaging staff pretty consistently without any explanation.''

Thompson, 65, will be able to get past the staff shakeups as long as there aren't more in the future, said Alex Vogel, a Republican strategist who worked with former Senate Majority Leader Bill Frist when he was considering a White House bid.

`Dividing Line'

``The dividing line is now that he's in,'' Vogel said. Thompson's decision to announce his intentions months after others in the field increases the pressure on his campaign, Vogel said. ``They have to execute perfectly out of the box.''

Some degree of staff change is normal, said Scott Reed, a Republican consultant who ran former Kansas Senator Bob Dole's 1996 presidential campaign. ``Most first-string campaign aides never make it to the fourth quarter,'' Reed said.

Another veteran of Dole's 1996 campaign, Republican consultant Craig Shirley, said Lacy's elevation ``is the best move Thompson's made to date.''

Thompson himself says the turnover is natural.

``We aren't forming a cabinet,'' he said in an interview last week. ``We are forming a presidential campaign, and that takes some time and you make adjustments along the way.''

Even so, Thompson has to show that he is capable of running a large operation, Republican pollster Whit Ayres said. Republican frontrunner Rudy Giuliani proved he has those skills when he was the mayor of New York, as did former Massachusetts Governor Mitt Romney, Ayres said.

Staff shakeups are ``more telling for him than for other candidates'' because Giuliani and Romney ``have significant experience and superb records as chief executives,'' said Ayres, who isn't affiliated with any of the campaigns. ``Senator Thompson's executive ability will be evaluated by how he structures his organization and runs his campaign.''

To contact the reporters on this story: Kim Chipman in Des Moines at kchipman@bloomberg.net; Kristin Jensen in Washington at kjensen@Bloomberg.net.

Last Updated: September 6, 2007 16:38 EDT