"If the other candidates can find common ground, I believe we can nominate a person who can win the general election and who will represent the values and policies of conservatism," he said. "Given the current delegate selection process, this means that I would vote for Marco Rubio in Florida, for John Kasich in Ohio, and for Ted Cruz or whichever one of the other two contenders has the best chance of beating Mr. Trump in a given state."
In arguing against the Republican front-runner, Romney warned Americans about the future, saying that Trump's "is the very brand of anger that has led other nations into the abyss."
"His domestic policies would lead to recession. His foreign policies would make America and the world less safe. He has neither the temperament nor the judgment to be president," Romney said. "And his personal qualities would mean that America would cease to be a shining city on a hill."
Trump implied Thursday that Romney's criticism was because he wished he was the one running for president. In fact, Trump said he's the reason that "choke artist" Romney decided to stay out of this year's race.
Laying into the New York businessman's proposals, Romney said he had concluded Trump is "very, very not smart" when it comes to foreign policy, and his economic plans would sink the country "into a prolonged recession."
In fact, Romney attacked Trump's business acumen, highlighting past business bankruptcies and failed ventures.
In addition to Romney's comments, his former vice-presidential candidate, House Speaker Paul Ryan, said he would speak out in the presidential race if he saw "conservatism being disfigured" in campaign rhetoric.