Michael Bloomberg's campaign announced a new strategy for attacking Bernie Sanders on Monday, on the basis of the senator's mixed record on gun control.

Bloomberg's campaign will run an ad on social media, launch a bus tour in Oakland, California, and roll out several surrogates to criticize Sanders.

Sanders was previously attacked in the 2015 for his record on guns.

The NRA had supported his 1990 campaign for Congress, and he had voted against the Brady Bill while in the House. But Sanders also supported other gun control legislation, according to PolitiFact.

Sanders has embraced several parts of the gun control movement in his 2020 campaign, calling for the expansion of background checks, a ban on certain guns classified as assault weapons, and more.

The Vermont senator has won the last two primary contests and is leading in several major national polls. It remains to be seen whether Bloomberg's attack will put a dent in his momentum.

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Michael Bloomberg's newest attack on Bernie Sanders is an old one.

On Monday, days after the Vermont senator emerged victorious in the Nevada caucuses, Bloomberg's campaign announced that they were beginning a multifaceted attack on Sanders' gun control record, which includes an advertisement that will run on social media, a bus tour that will roll out in Oakland, California, and several surrogates.

The strategy revisists one of the issues that dogged Sanders in the 2016 Democratic primary, and the attack is being leveled by one of the most prominent backers of gun control legislation in the country who has burned through over $500 million in media spending on his campaign with no signs of slowing down.

But Sanders has since brought his policy positions more in line with stringent gun control advocates, and after his strong performances in the early states, it remains to be seen if Bloomberg's latest attack will be enough to halt him.

Bloomberg's campaign released an advertisement on social media that cited Sanders' support from the National Rifle Association during his 1990 Congressional campaign, and his votes against the Brady Handgun Violence Prevention Act, which implemented federal background checks and a mandatory waiting period on unlicensed individuals seeking to purchase a handgun.

Bloomberg's account also sent out several other tweets criticizing Sanders' record on Monday. The campaign is also considering other options, such as sending their surrogates out on television to attack Sanders, CNBC reported.

"With gun violence becoming a regular part of American life Bernie Sanders stood on the sidelines," Bloomberg's campaign manager Kevin Sheekey said in a statement. "That's why we need Mike Bloomberg who has shown time and time again he's not afraid of taking on the NRA."

Sanders hails from a state where nearly 30% of the population owns guns, according to CBS News, and the state has a strong culture of using these weapons for hunting.

The NRA did support Sanders in 1990, the Washington Post reported. He also voted against certain provisions as the Brady Act was making its way through Congress, and against the final version of the Act in November 1993.

"If you passed the strongest gun control legislation tomorrow, I don't think it will have a profound effect on the tragedies we have seen," Sanders told Vermont publication Seven Days in 2013.

But Sanders has also voted for gun control legislation over the years, PolitiFact reported, leading to a mixed record that has been ripe for attack from his Democratic rivals.

Sanders faced questions about his record when he entered the Democratic primary in 2015 from the press and from other candidates. That year, a super PAC backing former Maryland governor Martin O'Malley released an ad with nearly the same charges that Bloomberg leveled this week.

"We need a sensible debate for gun control which overcomes the cultural divide that exists in this country and I think I can play an important role in this," he told CNN's Jake Tapper in July 2015.

As he makes another bid for president, Sanders appears to have brought his gun policy stances more in line with what other Democratic gun control advocates have pressed for in recent years. On his 2020 campaign website, he vows to "take on the NRA and its corrupting effect on Washington." He also supports expanding background checks, an assault weapons buyback program, and prohibiting high-capacity magazines, among other stances.

In March 2019, Sanders got into a fight with the NRA after calling for the US to ban the sale of assault weapons in the wake of the deadly New Zealand mosque attack.

Sanders is currently leading the rest of the Democratic field. He essentially tied former South Bend, Indiana mayor Pete Buttigieg in Iowa, and has won the New Hampshire primary and Nevada caucuses back to back.

Bloomberg's criticism potentially has more of a punch than other detractors, however. The billionaire has clout within the gun control activism community for his founding and funding of Everytown for Gun Safety, which works to pass and promote gun control legislation. He has also won the endorsement of two of Congress' most prominent gun control supporters: Florida's Ted Deutch, who represents the district, and Georgia's Lucy McBath, who lost her son in a fatal shooting and has become the public face of the House Democrats' push for gun control legislation.