He's in.
Washington Post
Actor and former senator Fred D. Thompson confirmed yesterday that he is running for president, ending a political flirtation he has been conducting since March and thrusting himself into the thick of the battle for the Republican nomination.
In a conference call with elected officials and party leaders backing his bid, Thompson campaign manager Bill Lacy said Thompson has finished "testing the waters" and will file papers making his candidacy official next Thursday. Thompson will announce his decision on that day in a webcast, with the campaign encouraging supporters nationwide to attend house parties on that day as the former lawmaker from Tennessee begins a trek through the early-voting states of Iowa, New Hampshire, South Carolina and Florida.
Washington Post