Former Republican presidential nominee and Arizona Sen. John McCain will not be endorsing any GOP candidate this election cycle.

"I've definitely decided that I won't endorse in this race," McCain told WPRI, CBS News' Providence, Rhode Island affiliate. "I've got my own race to run, which I view as being a very, very tough race and a great challenge, and I've got to spend my time and effort in what's going to be a very tough political campaign."

After speaking with the Arizona Republican Thursday afternoon, WPRI reporter Ted Nesi tweeted out McCain's position:

.@SenJohnMcCain tells me he has made up his mind & will not endorse any GOP'er for prez (but will back nominee). Focusing on own reelection. — Ted Nesi (@TedNesi) January 21, 2016

McCain said his decision was not a sign of disrespect toward any of the candidates.

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"I have great admiration for Jeb Bush," he said. "I like Chris Christie. John Kasich and I served together in the United States Senate - he's been a very successful governor. I'm sure there are a couple others there."

Despite his reluctance to support a particular contender, McCain has occasionally weighed in on the state of the Republican primary.

Earlier this month, the former GOP nominee said Texas Sen. Ted Cruz's citizenship -- and eligibility to run for the White House -- was an issue "worth looking into," after GOP front-runner Donald Trump questioned his rival's qualifications.

On Wednesday, McCain told reporters that he had not considered endorsing anyone because "I've got my own race to run." He did, however, mention that he still had "respect" for his former running mate, Sarah Palin, a day after her own endorsement of GOP front runner Donald Trump.

McCain backed his longtime Senate colleague and friend Lindsey Graham long before Graham officially entered the presidential race.

"He's a dark horse -- keep an eye on him!" McCain said last January. "In debates, he'll shred 'em. Have you see ever seen Senator Graham in a debate, on the floor of the Senate? He will do wonderful. I don't want to raise expectations, but I'm confident."

The South Carolina senator dropped out of the 2016 race last month.