Senator-elect Mitt Romney said Wednesday that he will not be running for the White House in 2020 against President Trump, and he said his days of running for the post are in his past.

"No. You may have heard I ran before," Romney told CNN in an interview when asked about a possible 2020 run. "I've had that experience."

"By the way, I acknowledge the president was successful, and I was not. He did something I couldn't do: He won. I recognize that and appreciate that," Romney added. "But no, I'm not running again. We'll see whether someone else does in a Republican primary or not, but time will tell."

The 2012 GOP nominee added that he is not ready to endorse the president's 2020 re-election bid and that he wants to "see what the alternatives are" to the president's candidacy.

"He was endorsing me. I wasn't endorsing him," Romney said, referring to his 2018 Senate bid that Trump supported. "I haven't decided who I'm going to endorse in 2020. I'm going to wait and see what the alternatives are."

Romney's comments came after a 24-hour war of words with Trump and his allies after the Utah Republican released an op-ed in the Washington Post declaring that the Trump presidency "made a deep descent" in December and that his character has fallen short during his time in the White House.

Trump fired back at Romney early Wednesday by wondering if he would be a second coming of Sen. Jeff Flake, R-Ariz., who was a frequent critic of the Trump administration. Trump said Romney instead should be a "TEAM player" for the GOP.

Even more biting was the reaction from RNC Chairwoman Ronna McDaniel, Romney's niece, who tweeted out that it is "disappointing and unproductive" to have a "incoming Republican freshman senator" attack the president.

Romney said he was not surprised by McDaniel's comments, given her post atop the GOP and role to support the president's agenda.

"No. She's the chairwoman of the Republican Party. She has a responsibility," Romney said. "I respect her right to express that viewpoint. It's probably more, if you will, civil than it would have been across the Thanksgiving dinner table because we, of course, have disagreements in our family. But she's a very loyal Republican, loyal to the president and she's doing what she thinks is best for him and for the party."

The comments are the latest in the roller-coaster history between the two Republican heavyweights, which dates back to Trump's endorsement of Romney during his 2012 presidential campaign and subsequent falling out throughout the 2016 campaign for Trump.