"Now more than ever American needs leaders with the strength of conviction," Cheney wrote in a statement released by the Rubio campaign. "That is why I am proud to endorse Marco Rubio."

Cheney also took time to blast Governor Charlie Crist and question Rubio's Republican primary rival.

"Charlie Crist has shown time and againt that he cannot be trusted in Washington to take on the Obama agenda because on issue after issue he actually supports that agenda," Cheney says. "Lately it seems Charlie Crist cannot be trusted even to remain a Republican."

Crist said earlier this week he is considering abandoning the Republican primary and launching an independent bid for the Senate. Polls show Crist trailing Rubio by more than 20 points in the primary, but keeping the race much closer in a three-way race that also includes Democrat Kendrick Meek.

"I strongly urge him to either stay in the Republican Primary or drop out of the race," Cheney said of a possible independent campaign. "The only winners from an independent bid by Crist would be Barack Obama and Harry Reid."