Tom Coburn left the U.S. Senate last year to wage a battle against cancer (he’s doing well). But the Oklahoman remains a beloved and respected conservative who was renowned for his integrity in the Senate (remember the “Bridge to Nowhere” and his standing up to Harry Reid).

He has now decided to endorse a candidate on the eve of Oklahoma’s primary. Yesterday, he endorsed Marco Rubio while at the same time asserting that Donald Trump was “perpetuating a fraud.”

“We need a president who will reawaken our belief in the American idea and not merely complain about how things are but challenge us to dream of what could be,” Coburn said in a statement. He plans to campaign with the Florida senator today in Oklahoma.

Coburn contrasted Rubio with Trump:

His empty promises, bullying, and bloviating rhetoric will only deepen the frustration and disillusionment that gave rise to his campaign. He simply lacks the character, skills, and policy knowledge to turn his grandiose promises into reality.

Coburn has certainly had his differences with Rubio in the past. He strongly opposed the “Gang of Eight” immigration bill that Rubio sponsored in 2013. But overall Coburn says the choice is clear: “(He) has been an extremely effective tea-party senator. No candidate running for president has fought Obamacare more effectively than Marco and no one has a better grasp of foreign affairs and America’s place in the world.”