ST. PAUL, Minn. —Fred Thompson, a Republican, sidestepped questions yesterday about the departure of yet another high-level aide to his presidential campaign-in-waiting. Linda Rozett, a longtime U.S. Chamber of Commerce official, is gone from the former Tennessee senator’s committee to “test the waters” of a presidential bid after spending several weeks as communications director.

“I don’t know what the story is,” said Mr. Thompson, who was asked about the departure while campaigning at the Minnesota state fair. Ms. Rozett’s departure was disclosed in an e-mail to staffers from campaign manager Bill Lacy.

“It is my duty to let you know that Linda Rozett is no longer with our committee,” Mr. Lacy wrote. “I will have to make a lot of tough decisions to make our venture successful, and this was one of them. Linda is a talented, professional, and gracious lady who will be missed. But in the limited amount of time we have, I feel it critical to have a communications point person with significant campaign experience.”

The all-but-declared candidate collected about $1.5 million less than the $5 million backers had hoped to bring in during June, his first fund-raising month. In July, Mr. Thompson sidelined his campaign-manager-in-waiting, Tom Collamore, and watched a few other aides follow him out the door amid consternation inside the operation about the active role of Mr. Thompson’s wife, Jeri.