Fred Thompson's campaign for president has collapsed.Well, at least, among the bookies. I've been giving readers regular updates on the betting in the presidential election, but absolutely nothing has been more dramatic this fall than Thompson's market meltdown. According to the betting at the Iowa Electronic Markets, the TV actor's chances of winning the GOP nomination have slumped in just six weeks from nearly 30% to less than 10%. As recently as June, just after the former Senator announced he was running, he was the favorite in the betting, at nearly 40%. The numbers are similar over at Dublin-based betting exchange InTrade. Thompson was at 35% in July. Today? 6%. Credit the old Wall Street saw: Buy on the rumor, and sell on the news. Before Thompson jumped into the race, conservative columnist George Will compared the anticipation to "Tulipmania." He questioned whether the Law & Order star really offered either the charisma, or the Mr. Conservative credentials, that his boosters claimed. Maybe Thompson could never have matched the elevated expectations that greeted him. But his lackluster campaign and weak debate performances have brought him down to earth with a thump. The betting now puts the Republican race between two people. The markets give Rudy Giuliani a 40% chance of winning the nomination, and former Massachusetts governor Mitt Romney a 30% chance.