“Our country is at a crossroads facing threats from abroad and attempts from within to restructure the very foundation of our freedoms," Cheney said in a statement.
"America requires leaders to face down these challenges who are confident in who they are and what they stand for. Leaders who know that public service is about something bigger than climbing the political ladder and amassing greater political power."
Cheney also took a shot at Florida Republican Gov. Charlie Crist, who according to reports is mulling an Independent bid for the Senate against Rubio, who he trails badly in GOP primary polls.
"Lately it seems Charlie Crist cannot be trusted even to remain a Republican. I strongly urge him to either stay in the Republican Primary or drop out of the race. The only winners from an independent bid by Crist would be Barack Obama and Harry Reid," Cheney said.
Cheney previously endorsed Trey Grayson over Rand Paul in the Kentucky GOP Senate primary.