Former Sen. Rick Santorum lit into Ohio Gov. John Kasich for not backing Republican presidential nominee Donald Trump, citing the pledge that all candidates signed last year pledging their support for the eventual GOP nominee.

Santorum told CNN that he's not pleased with Kasich, former Florida Gov. Jeb Bush and House Speaker Paul Ryan — who has been tepid in his support for Trump but voted for him anyway — for not supporting the GOP nominee.

"I'm not happy with either John Kasich or Paul Ryan on the way they're conducting themselves — particularly John Kasich," Santorum said. "I'm going to say to John Kasich, if you're watching — John, you signed a pledge. You signed a pledge saying that you would support the Republican nominee for president. You signed a pledge in order to get on the ballot in South Carolina. You promised that you would follow through on that, and you know Donald Trump had a chance because he was leading in the polls at the time to be our nominee, and you signed it anyway."

"You can't say a man who's not going to keep his word is someone that should, frankly, be paid attention to when it comes to how he's going to vote," Santorum continued. "John, you are better than that. John was a dear friend in Congress, and I know John Kasich is better than that. Jeb Bush, I would say the same thing to you. You signed a pledge! I would say the same thing to other candidates who have not stepped forward and said. 'I'm going to support Donald Trump' because you wouldn't [have] been on the ballot, you wouldn't have been able to run for president had you not signed that pledge."

"And if you're out there saying, 'well he's got character that's beneath the dignity of the office,' what about that character?" Santorum charged. "What about the character — I'm going to tell your kids and grandkids that you signed a pledge. You gave your word to be president of the United States, to run for president of the United States and backed away from it. Shame on them."

Santorum, who supported Sen. Marco Rubio in the GOP primary after he dropped out, has been a supporter of Trump's since late May. The former two-term Pennsylvania senator has been an outspoken advocate of Trump's since that time, specifically arguing that the real estate mogul has a chance to pull off an upset in Pennsylvania.

The runner-up to Mitt Romney for the 2012 GOP nomination did say that he was uncomfortable with the comments that were unearthed last month, in which Trump talks about grabbing women "by the pussy" and using his celebrity to seduce them. He added that he is not someone he wants his children to emulate.

"No, I'm not comfortable with some the things that he says and some of the things he's done," Santorum said. "I find it disgusting and [I'm] not going to do anything publicly to try to make excuses for it."

"When I look at this race, I see candidates both from a character point of view who have some serious problems. Hillary Clinton has some serious problems telling the truth and secrecy, and pay for play and all the other things that come with being an insider in Washington D.C., and making, by the way, hundreds of millions of dollars doing it," Santorum said. "I look at Donald Trump and I see, just as you mentioned, a man whose character is not exactly what I want to recommend to my kids to emulate, so I've got problems with both on character."