Former Oklahoma Republican Sen. Tom Coburn endorsed Florida GOP Sen. Marco Rubio for president Monday, one day before Oklahoma’s Super Tuesday primary.

While he served in the Senate, Coburn was known for his annual “Wastebook,” a list of outlandish or bizarre projects that the government funded with taxpayer dollars.

In his endorsement of Rubio, Coburn also issued a blistering rebuke of Republican presidential front-runner Donald Trump, calling his campaign a “fraud.”

Former Sen. Tom Coburn (R-OK) speaks during a news conference on December 17, 2013 on Capitol Hill in Washington, DC. Sen. Coburn held the news conference to release 'Wastebook 2013,' his annual report of 'examples of wasteful and low-priority spending' of the U.S. government. (Photo by Alex Wong/Getty Images)

Former Oklahoma Republican Sen. Tom Coburn (Alex Wong/Getty Images)

“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. “At a time when our republic, and the Republican Party, is at a crossroads I have no doubt that the right choice for America is Marco Rubio.”

“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,” Coburn said. “Marco would be such a president. I urge voters in Oklahoma and across the country to take a stand for freedom and stand with Marco on Tuesday and throughout this campaign.”

Coburn called Rubio “the only candidate in this race who is in the mold of President Reagan.”

“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 Washington, Marco 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.”

Coburn said that he understands “the depth of the American people’s frustration with the status quo” but added that Trump isn’t the answer.

“Voters are right to be upset with the direction of the country,” Coburn said. “And even though the ranks of conservatives in Washington have grown, the pace of change simply isn’t fast enough. 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 echoed Rubio’s recent assertion that Trump is a “con artist” who is leading the American people to believe that he is a conservative when he is not.

“Donald Trump’s campaign is a fabrication,” Coburn said. “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.”

“Put simply, Donald Trump has no plan to make America great again,” Coburn concluded. “He is a populist without portfolio.”