There is some evidence to suggest Thompson would hurt Romney, one of the three front-runners in Iowa, by entering the race.
It comes by comparing two polls of likely GOP caucus-goers taken during May. The Iowa Poll, taken by the Des Moines Register, did not include Thompson, who has not formally announced. But the American Research Group poll, taken by a Manchester, NH research firm, did include Thompson.
When you compare the findings of the two polls, Rudy Giuliani and John McCain actually increase their support if Thompson is in the race. Romney drops.
Giuliani got 17 percent in the Thompson-free Iowa Poll. He gets 23 percent in the Thompson-included ARG poll. McCain’s numbers were 18 percent in the Iowa Poll and 25 percent in the ARG.)
By contrast, Romney scored 30 percent in the Iowa Poll that did not include Thompson. But he dropped to 16 percent in the ARG poll that included Thompson. That’s a drop of close to 50 percent so it seems clear Thompson is taking a least a little something away from Romney here.