Rep. Connie Mack IV’s official entrance into Florida’s Senate race Monday and his position as sudden Republican frontrunner poses a unique strategic challenge to his top GOP rivals, former Sen. George LeMieux and former state House Majority Leader Adam Hasner.

While Mack has focused on attacking two-term Democratic Sen. Bill Nelson, his rivals have begun to train their fire on Mack — but in different ways.

In separate interviews with Roll Call, LeMieux was more direct while Hasner shied away from a frontal attack.

“This is going to be a contrast between celebrity and substance,” LeMieux said. “I hope that I proved in the 16 months I was in the U.S. Senate that I was a substantive Senator that brought forth solutions. … That will be the distinction between the Congressman and myself.”

Hasner said he will continue to introduce himself to voters and talk about his conservative record.

“I don’t want this to be about people voting against somebody. What I want is for people to look at our campaign, look at my record,” he said. But his campaign released a polling memo Wednesday showing Mack’s support to be soft.

“Republicans do not favorably associate Mack with any issue or accomplishment,” pollster Gene Ulm of Public Opinion Strategies wrote in the memo.

In a conference call with reporters earlier this week, Mack stuck to knocking Nelson as a liberal.