Rick Santorum unloads on John Kasich, Jeb Bush for not voting for Donald Trump: 'Shame on them!'

Former Pennsylvania Sen. Rick Santorum — who sought the Republican presidential nomination in both 2012 and 2016 — unloaded on Ohio Gov. John Kasich and other GOP primary candidates who've refused to back nominee Donald Trump.

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Santorum went on the rant after being asked about what he thought of Trump's character, particularly after the leaked 2005 tape from mid-October showed the Manhattan billionaire boasting of being able to make sexual advances on women without their consent because he was famous. Santorum said that was abhorrent, but Democratic nominee Hillary Clinton also has character flaws.

After knocking Kasich and House Speaker Paul Ryan for "how they're conducting themselves" this general election cycle, he homed in on the Ohio governor. On Monday, Kasich said he had cast a write-in ballot for president, voting for Sen. John McCain of Arizona, the 2008 Republican nominee.

"I want to say to John Kasich, if you're watching: John, you signed a pledge! You signed a pledge saying you would support the Republican nominee for president. You signed a pledge to get on the ballot in South Carolina. You promised that you would follow through with that, and you knew that Donald Trump had a chance because he was leading in the polls at the time to be our nominee, and you signed it anyway," Santorum said.

He said Kasich's voting decision should "frankly" not "be paid attention to" because he "can't keep his word."

Kasich ended any chance of backing Trump following the release of the 2005 tape, which he admitted the contents of were not that surprising to him.

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"John, you are better than that," Santorum said. "John was a dear friend in Congress and I know John's 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.'"

The Pennsylvania Republican insinuated that candidates who believe Trump's character is "beneath the dignity" of the presidency, don't have any room to talk because they're abandoning the pledge to support the GOP nominee.

"I'm going to tell your kids and grandkids that you signed a pledge to run for president and backed away from it," he said. "Shame on them."

Watch Santorum's rant below: