Rudy Giuliani, the personal attorney for President Trump, on Thursday, called on conservative writer Bill Kristol to apologize for accusing him of lacking the courage to face the “stronger person” Hillary Clinton in New York's 2000 senate race and completely omitting the fact that he was diagnosed with prostate cancer at the time.

Kristol, an anti-Trump critic, on Sunday called out the former New York mayor for hypocrisy, saying he played “a tough guy” on Twitter but lacked the nerve to take on Clinton in his home state. “When the race got tough, @RudyGiuliani got going. As bullies do when confronted by a stronger person,” he tweeted.

So this is not your best work

— Twitter user reaction to Bill Kristol's tweet

Giuliani told “America This Week” that his father died from prostate cancer and he was forced to undergo two different treatments that wore him out. He said he had to take a daily nap for two hours and “would get sick to his stomach at the most inappropriate times.” He said he was only able to continue his job as mayor because of his dedicated staff.

"If that man doesn’t apologize, there’s nothing left of decency with him," Giuliani said in an interview.

It took little time for social media to jump on Kristol’s comment and point out Giuliani’s cancer diagnosis.

“Well...he was diagnosed with prostate cancer during the race. So this is not your best work,” tweeted Nathan Wurtzel. “You do recall that he was diagnosed with prostate cancer that same year?” seconded radio personality Frank Morano.

Giuliani announced in 2000 during a press conference that the reason he was suspending his Senate campaign, as he was facing a serious competition from Clinton, due to health reasons, particularly the prostate cancer diagnosis, which he went on to beat years later.

“I used to think the core of me was in politics, probably,” he said. “It isn't. When you feel your mortality and your humanity you realize that, that the core of you is first of all being able to take care of your health.”

Fox News' Lukas Mikelionis contributed to this report