Congressman Connie Mack, whose Senate campaign has lost luster in the eyes of some Republicans, is scheduled to get a big endorsement Tuesday from the American Conservative Union, the nation's largest grassroots group, the Associated Press Reports.

The endorsement comes none too soon for Mack, who is favored by FreedomWorks but has failed to inspire a show of support from the Club for Growth. State CFO Jeff Atwater is mulling whether to enter the race, but an ACU endorsement will probably give him pause.