A top aide to Fred Thompson resigned Tuesday.
WASHINGTON (CNN) - A top adviser to possible Republican presidential candidate Fred Thompson has submitted his resignation, Republican sources told CNN Tuesday.
Tom Collamore joined the nascent Thompson effort after being recruited away from his post at Altria, the parent company of such brands as Kraft Foods and Philip Morris.
The Thompson campaign said that former GOP Sen. Spencer Abraham - who served as Energy Secretary from 2001 to 2005 - would come aboard in a top campaign role along with veteran Florida Republican strategist Randy Enright.
A campaign spokeswoman said Collamore would remain as a senior adviser.
In a telephone conversation with CNN, Collamore confirmed he has resigned from his position at Friends of Fred Thompson.
"It was an honor to be part of getting things started, and I believe I helped get things ready for the next level," he said.
Collamore is a GOP campaign veteran who was tasked with assembling a Thompson campaign operation. His experience dating back to the Reagan-Bush years was touted by Thompson allies as a sign the former senator was serious
about joining the race and building a top flight organization.
He told CNN he was prepared to stay on in an official capacity but that he was "very respectful of the desire of Fred and Jeri to make some changes as they move to the next level."
Several GOP sources familiar with the decision - and the additions to the Thompson staff - acknowledged differences between Collamore and Thompson's wife, Jeri, on structure and staffing.
"It was not hostile by any means, but she is very involved and there were clear differences," one source close to the situation told CNN.
"She is running the operation," said a senior GOP source who is close to Collamore.
Abraham, before being elected to the Senate from Michigan in 1994, was a top political aide to Vice President Dan Quayle. He was defeated in his bid for re-election to the Senate in 2000.
- CNN Chief National Correspondent John King