The main super-PAC backing Democratic presidential candidate Hillary ClintonHillary Diane Rodham ClintonPelosi planned on retiring until Trump won election: report Pence autobiography coming from Simon & Schuster Amanda Gorman makes the cover of Vogue MORE released another Web ad on Thursday, knocking GOP hopefuls for continuing to pledge support to Donald TrumpDonald TrumpRomney blasts end of filibuster, expansion of SCOTUS McConnell, GOP slam Biden's executive order on SCOTUS US raises concerns about Iran's seriousness in nuclear talks MORE if he wins the Republican nomination. 

The ad, which is part of Priorities USA’s $1.5 million campaign called “Wrong for Us,” targets all Republican candidates for not standing up to the GOP presidential front-runner after his latest proposal to temporarily ban Muslims from entering the United States. But many Republicans were quick to criticize Trump’s controversial plan.   

“The Republican candidates for President are all trying to tell us how strong they are,” the ad says in text over pictures of the top GOP candidates, Sen. Ted CruzRafael (Ted) Edward CruzGOP lawmakers block Biden assistance to Palestinians Cruz on Boehner: 'I wear with pride his drunken, bloviated scorn' The Hill's Morning Report - Biden: Let's make a deal on infrastructure, taxes MORE (R-Texas), Sen. Marco RubioMarco Antonio RubioHillicon Valley: Amazon wins union election — says 'our employees made the choice' Overnight Defense: Biden proposes 3B defense budget | Criticism comes in from left and right | Pentagon moves toward new screening for extremists The growing threat of China's lawfare MORE (R-Fla.) and retired neurosurgeon Ben Carson. 

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“But they’re showing themselves to be quite weak. They all seem to be afraid of Donald Trump," the ad continues, playing a video of tigers brawling, which then cuts to video of kittens fighting. 

The ad continues, “If they can’t even stand up to Donald Trump, why would anyone think they’re strong enough to lead America?”

Priorities USA spokesman Justin Barasky said in a statement, “The political cowardice by the GOP field makes you wonder why anyone would believe they’re strong enough to lead America when they’re not even strong enough to stand up to someone who’s putting the safety of our nation at risk.” 

The video, released two days after the last GOP debate of 2015, comes at a time when national security has taken center stage and presidential hopefuls are seeking to display their experience on the matter amid terror attacks in Paris and San Bernardino, Calif.