The biggest target for Democrats at their kick-off 2016 debate wasn't Donald Trump or Tea Party Republicans: It was the NRA. 

Throughout the roughly two-hour tangle on stage, the candidates vied to demonstrate their gun control chops and flaunt their disdain for the gun lobby. While Vermont Sen. Bernie Sanders was put on his heels for siding with the gun industry in the past, even the rural-state lawmaker defended himself by pointing out how he's no friend of the NRA, either. 

"Bernie Sanders has a D-minus [rating] from the NRA," Sanders noted. 

But he was soon outdone by former Maryland Gov. Martin O'Malley, who countered: "I have an F from the NRA, senator." 

Asked later which "enemy" he's most proud of, O'Malley answered: "The National Rifle Association." Hillary Clinton also included the NRA on her enemies list. 

Coming after a string of tragic mass shootings, the debate showed Democrats refocusing their message on the need for gun laws, something the Obama administration has been unable to pass through a Republican-led Congress. But while legislative efforts have stalled on Capitol Hill, the NRA delivered a sharp, point-by-point counter -- over Twitter -- to most of the gun statements on stage in Las Vegas Tuesday night. 

After O'Malley boasted about his failing NRA rating, the group tweeted: 

As for the mention on O'Malley and Clinton's enemies list, they tweeted: 

Gun control emerged as the main issue that caused headaches Tuesday for Sen. Sanders, whom Clinton accused of being weak on gun laws. 

She criticized him for voting for a 2005 bill giving gun manufacturers immunity from lawsuits. After Sanders described that bill as complicated, she said, "It wasn't that complicated to me." 

She said, "It's time the entire country stood up against the NRA." 

Sanders responded, "All the shouting in the world" is not going to end the violence. He said the country needs to reach a consensus, and stressed that rural states view gun laws differently than other states. 

Sanders said he does want to toughen background checks and said, "We've got to move aggressively at the federal level in dealing with the straw man purchasers." 

The NRA fired back: 

The NRA wasn't the only group in Democrats' sights Tuesday night at the CNN debate. Former Rhode Island Sen. Lincoln Chafee named the coal lobby as the enemy he's most proud of. 

Sanders cited Wall Street and the pharmaceutical industry. 

Former Virginia Sen. Jim Webb may have given the most talked about answer, though: "I'd have to say the enemy soldier that threw the grenade that wounded me, but he's not around right now to talk to."