In the latest weekly Rasmussen Reports 2008 Republican presidential primary poll, Thompson trailed frontrunner Rudy Giuliani by just one point, 24-23 percent.

Giuliani, the former New York City mayor, has been at either 24 or 25 percent for five of the past six weeks, according to Rasmussen's surveys. Thompson rebounded slightly this week after polling strong in June and July. Former Massachusetts Gov. Mitt Romney was in third place with 13 percent, just ahead of Sen. John McCain at 12 percent. Former Arkansas Gov. Mike Huckabee remained in fourth at 5 percent, ahead of Sen. Sam Brownback and Reps. Ron Paul, Tom Tancredo and Duncan Hunter.

After signaling his interest in the nomination in March, Thompson aides initially said he would announce his candidacy around the Fourth of July. Later the date was moved to after Labor Day.

Some supporters have worried he has waited too long to take advantage of a wave of interest accompanying initial reports of his potential candidacy.

Evidence of campaign disorganization and staff turmoil have raised questions among Republican insiders about whether Thompson has sufficient discipline and zeal or the ability to craft a message that separates him from the field.