Another one of Donald Trump's former GOP rivals is falling in line.

Former Texas Gov. Rick Perry, who less than a year ago called the presumptive GOP nominee a "cancer on conservatism," threw his support behind Trump Thursday evening.

"He is not a perfect man," Perry told CNN by phone. "But what I do believe is that he loves this country and he will surround himself with capable, experienced people and he will listen to them."

Perry, who suspended his presidential campaign in September, had previously endorsed and campaigned for Texas Sen. Ted Cruz. He addressed the calls for him to run against Trump as a third-party candidate, saying it would be a "quixotic" effort.

Trump isn't Perry's first choice, he acknowledged, but said the business mogul is "one of the most talented people who has ever run for the president I have ever seen."

Asked if he would consider being Trump's running mate, Perry said yes. "I am going to be open to any way I can help," he said. "I am not going to say no."

When Perry announced his endorsement Thursday, his website still had a page titled, "Defending Conservatism Against the Cancer of Trump-ism" -- illustrating just what a reversal it is to see GOP leaders falling in line behind Trump after being highly critical of him in the past.