Giuliani now holds a 2-to-1 advantage over McCain among Republicans, according to the ABC News-Washington Post poll, more than tripling his margin of a month ago. The poll found Giuliani leading with 44 percent to McCain's 21 percent.
Gingrich ran third with 15 percent, while Romney was fourth with 4 percent.
The former House Speaker has not decided if he will enter the race, and without him, Giuliani's lead would increase even more, to 53 percent compared with McCain's 23 percent, according to the ABC News-Washington Post poll.
A Romney campaign spokesperson confirmed to ABC News that until recently the Massachusetts governor has "mostly refrained" from citing specific issue differences with Giuliani, focusing most of his fire on McCain.
Romney began his effort to position himself as the conservative candidate in the Republican presidential field in a September 2006 interview with the New York Times' Adam Nagourney in which he cited differences with the Arizona senator on immigration, campaign finance regulation, and the rules that need to be followed when interrogating suspected terrorists.
In a recent interview with Nightline anchor Terry Moran, Romney alluded to big differences between himself and Giuliani on "social issues."
The former Massachusetts governor added that such differences have a "bigger impact on the primary process" than they do in the general election.
Romney refrained, however, in his ABC News interview, from attempting to articulate specific policy differences with Giuliani calling him a "great friend," a "great leader," and a "great Republican."