A populist former senator who famously chronicled government waste and set the conservative austerity agenda blasted Donald Trump as “a populist without portfolio” in his endorsement of Sen. Marco Rubio (R-Fla.).

Sen. Tom Coburn (R-Okla.) resigned at the conclusion of the last Congress to focus on his fight against cancer.

Rubio had already been endorsed in early January by Oklahoma Sen. Jim Inhofe (R).

“Martin Luther King, Jr. once said, ‘Cowardice asks the question – is it safe? Expediency asks the question – is it politic? Vanity asks the question – is it popular? But conscience asks the question – is it right? And there comes a time when one must take a position that is neither safe, nor politic, nor popular; but one must take it because it is right,'” Coburn said in a statement today.

Coburn said he was picking Rubio because “America desperately needs a president who will appeal to people’s highest aspirations rather than their deepest fears; a president who will model servant leadership rather than self-promotion; and a president who will cast a vision and unite the country instead of denigrating dissenters as second-class citizens.”

“…Marco is the only candidate in this race who is in the mold of President Reagan. While some are offering a message of victimization and helplessness against Washington, Marco understands that ‘We the People’ are the establishment and the elites in American society. 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 added that Rubio “has been an extremely effective Tea Party senator” in Washington.

“As a physician, business owner, member of the Class of 1994 and later as a U.S. Senator, I came to understand the depth of the American people’s frustration with the status quo. Voters are right to be upset with the direction of the country. And even though the ranks of conservatives in Washington have grown, the pace of change simply isn’t fast enough,” he continued.

“The candidacy of Donald Trump, however, threatens to undo and reverse years of work that began with Goldwater and Reagan – work that future movements like the 1994 Republican Revolution and the Tea Party sought to preserve and perfect.”

Coburn slammed Trump’s campaign as “a fabrication.”

“He is perpetuating a fraud on the American people. 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,” he said. “Put simply, Donald Trump has no plan to make America great again.”

In tweets and at campaign events earlier this month, Trump said “very highly respected senator” Coburn called Sen. Ted Cruz (R-Texas) “one of the most dishonest people he’s ever worked with.”

Coburn said that was an “absolute fabrication.” He did say last October that Cruz gave supporters “a false hope” with his vow to end Obamacare, “knowing that you couldn’t accomplish it, but it was about yelling, and screaming, and waving the flag.”