“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 ObamaBarack Hussein ObamaDemocrats cannot afford to play hardball on immigration reform Trump's tariffs are a case of crony capitalism Obama to visit Kenya, South Africa for Obama Foundation in July MORE and Harry ReidHarry Mason ReidAmendments fuel resentments within Senate GOP Donald Trump is delivering on his promises and voters are noticing Danny Tarkanian wins Nevada GOP congressional primary MORE," Cheney said.

Cheney previously endorsed Trey Grayson over Rand PaulRandal (Rand) Howard PaulGOP senators call for probe of federal grants on climate change Overnight Health Care — Presented by the Association of American Medical Colleges — Key ObamaCare groups in limbo | Opioids sending thousands of kids into foster care | House passes bill allowing Medicaid to pay for opioid treatments US watchdog: 'We failed' to stem Afghan opium production MORE in the Kentucky GOP Senate primary.