It was pile on Donald Trump day on the Sunday morning interview shows, with Mitt Romney, Sens. Marco Rubio of Florida and Ted Cruz of Texas and Gov. John Kasich of Ohio all refusing to accept the inevitability of Trump as the Republican nominee.

Romney, the 2012 GOP standard bearer, declined to endorse any of Trump’s rivals, indicating he may do so after the March 15 primaries when the Rubio's and Kasich's respective home states cast their ballots. Kasich has said any candidate who cannot carry his home state should leave the race.

“I wanted to remain as a neutral umpire,” Romney said on CNN’s “State of the Union.” “But over the last several weeks some of the things Donald Trump has done … I just couldn’t wait any longer.”

The comments came in the wake of Saturday’s primaries and caucuses that saw Trump and Cruz each win two states. At the end of the night, Trump had a total of 382 delegates to 300 for Cruz, en route to the 1,237 needed for the nomination. Rubio has 128 and Kasich, 35.

trump U.S. Republican presidential candidate Donald Trump walks to the podium at a press event at his Trump International Golf Club in West Palm Beach, Florida, March 5, 2016 Photo: Joe Skipper/Reuters

Romney last week delivered a scathing attack on Trump, deriding his temperament, lack of coherent policies and business acumen, and calling the New York City real estate mogul a liar, fraud and dangerous to America’s future.

Romney said he never expected Trump to do as well as he has with the voting public but recognizes Trump has “tapped into an anger.” However, instead of building something with it, he has “taken it down a very dark alley.”

“He may be colorful. He made a lot of money for himself. He should not be president of the United States,” Romney said on NBC’s “Meet the Press.”

Romney also conceded Trump likely will be the party’s nominee, although he’s hoping for an “open convention.” He said he could support any of Trump’s remaining rivals, calling them all “real deal” Republicans. But, he said, he’s “not going to encourage the creation of a new party” should Trump gain the nod.

Trump said on CBS’s “Face the Nation” said he’s surprised by this stop-Trump movement and warned any third-party effort “would mean Hillary [Clinton] would win” in November. “They’re really playing with fire,” he said.

“If Donald is the nominee, it’s a catastrophe,” Cruz said on CBS’s “Face the Nation.” Cruz warned a brokered convention would result in “a manifest uprising” by angry voters.

Cruz blamed the media for Trump’s rise, saying reporters haven’t pressed him on releasing his tax returns. Cruz said he suspects there’s a “bombshell” in Trump’s returns, and that’s why he hasn’t released them.

Cruz criticized both Trump and Rubio for engaging in insults and mud-throwing and urged the candidates to stick to the issues.

rubio Republican U.S. presidential candidate Florida Senator Marco Rubio campaigns in Toa Baja, Puerto Rico, March 5, 2016. Photo: Alvin Baez/Reuters

Rubio refused to concede, criticizing Trump in a “State of the Union” interview for not attending the Conservative Political Action Conference, again questioning Trump’s conservative credentials and telling Republicans they “have to ask ourselves how we let” Trump take the lead.

“It’s not enough to say vote for me because I’m angrier and over the top, and I’m going to do and say things no one else will do,” Rubio said.

On ABC’s “This Week,” Kasich refused to agree it’s time for him to get out of the race and denied his strategy is to be a spoiler, pointing to the possibility of a multiple-ballot convention.

“I will win Ohio, and it will be a whole new ballgame,” Kasich said, discounting an NBC/Wall Street Journal/Marist poll indicating Trump is leading him in Michigan 41 percent to 13 percent.

Sen. Lindsey Graham, R-S.C., who abandoned his presidential bid late last year, said on “Meet the Press” it may be time to back Cruz as the way to deny Trump the nomination, even though he once compared Trump and Cruz to a choice between a bullet and poison.