One day after a report that Sen. Ted Cruz (R-TX) questioned Donald Trump’s “judgment” in a private event, Trump called out Cruz for criticizing him behind closed doors but refraining from negative comments in public.

Looks like @tedcruz is getting ready to attack. I am leading by so much he must. I hope so, he will fall like all others. Will be easy! — Donald J. Trump (@realDonaldTrump) December 11, 2015

.@tedcruz should not make statements behind closed doors to his bosses, he should bring them out into the open – more fun that way! — Donald J. Trump (@realDonaldTrump) December 11, 2015

Cruz has so far refrained from bashing Trump in public. After Trump announced his proposal to ban Muslims from coming to the United States, Cruz disagreed but stopped short of condemning Trump’s remarks.

But the Texas senator spoke about Trump and Ben Carson during a Manhattan fundraiser on Wednesday, according to the New York Times.

“Who am I comfortable having their finger on the button? Now that’s a question of strength, but it’s also a question of judgment. And I think that is a question that is a challenging question for both of them,” Cruz said of Trump and Carson.

Cruz has started gaining on Trump in the key primary state of Iowa, which may be making Trump uneasy. The real estate mogul has a habit of attacking his Republican rivals when they rise in the polls, as both the New York Times and the Wall Street Journal noted this week. Trump may have released his proposal to ban Muslims from entering the country in an attempt to boost his support with evangelical voters in Iowa.