Republican presidential candidate Donald Trump on Sunday hit back on Hillary Clinton’s claim that Islamic jihadists are using his anti-Muslim rhetoric as a recruiting tool, calling the Democrat a “liar” and a string of other insults.

At the heart of the dispute: Clinton’s contention during Saturday night’s Democratic debate that Trump is “becoming ISIS’ best recruiter.”

“They are going to people showing videos of Donald Trump insulting Islam and Muslims in order to recruit more radical jihadists,” Clinton said during the televised debate on ABC. “So I want to explain why this is not in America’s interest to react with this kind of fear and respond to this sort of bigotry.”

While experts say it’s likely that Trump’s call for a temporary ban on Muslims entering the United States could be used by ISIS, independent fact-checkers have not found evidence of videos as described by Clinton.

“It’s nonsense. It’s just another Hillary lie,” Trump said on NBC’s Meet the Press. “She lies like crazy about everything, whether it’s trips where she was being gunned down in a helicopter or an airplane, she’s a liar and everybody knows that. But she just made this up in thin air.”

At 4:05 a.m. Sunday, Trump tweeted: “Hillary Clinton lied when she said that “ISIS is using video of Donald Trump as a recruiting tool.” This was fact checked by @FoxNews: FALSE.”

But, under questioning from Meet the Press host Chuck Todd, Trump said he would not tone down his language, even if he discovered his words were being used in recruitment videos.

“I think that my words represent toughness and strength,” he said. “Hillary’s not strong, Hillary’s weak, frankly. She’s got no stamina, she’s not nothing.”

On Sunday, Clinton communications director Jennifer Palmieri said her boss was not “referring to a specific video” and added that groups monitoring ISIS say that Trump already is a social media propaganda tool for jihadists. Palmieri spoke on ABC’s This Week.