The political action committee (PAC) supporting Jeb Bush's White House bid is using a new television ad to aggressively go after the former Florida governor's key GOP rivals -- Donald Trump, Ted Cruz and Marco Rubio.

The spot, titled "Desk" and set to be broadcast in key early voting states, alludes to the Dec. 2 shooting in San Bernadino, California that claimed the lives of 14 individuals and injured more than 20 others, according to Reuters.

"When the attacks come here, the person behind this desk will have to protect your family," a narrator says, with the voice set to images of the presidential desk in the Oval Office of the White House.

The commercial, paid for by the deep-pocketed Right to Rise super PAC, then asks voters to consider what would happen if the man behind the desk were one of Bush's challengers.

"Will he be impulsive and reckless, like Donald Trump?" the ad asks "Will he have voted to dramatically weaken counter-terrorism surveillance, like Ted Cruz? Will he have skipped crucial national security hearings and votes just to campaign, like Marco Rubio?"

The spot then moves on to praise Bush, casting him as a steady, experienced choice for the GOP nomination, CNN noted.

"Twenty-seven generals and admirals support Jeb Bush, because Jeb has the experience and knowledge to protect your family," it proclaims.

The Bush camp seems intent on upping the ante, after the latest national polls have revealed troubling approval numbers for the candidate.

Trump, at least, seems ready to fire back. The real estate tycoon is threatening to sue a Bush supporter who published a Miami Herald ad slamming him as a "narcissistic BULLYionaire," the newspaper reported.

"Though we believe your decision is fool hearted (sic)," Trump general counsel Alan Garten warned Bush donor Mike Fernandez, "please be advised that [if] your ads contain any false, misleading, defamatory, inaccurate or otherwise tortious statements and representations concerning Mr. Trump, his businesses or his brand, we will not hesitate to seek immediate legal action."