With less than a month to go until the Iowa caucuses, the top two Democratic candidates' campaigns are taking pot shots at each other on gun control.

On Friday, John Podesta, the chairman of Hillary Clinton's presidential campaign took aim at her closest threat, Bernie Sanders, highlighting the Vermont senator's murky history with gun control.

In a tweet, Podesta cited a 2005 Senate vote on the Protection of Lawful Commerce in Arms Act, a National Rifle Association-backed bill that protected gun manufacturers from lawsuits when their guns are used in crimes. Then-Sens. Clinton and Barack Obama voted against it. Sanders voted for it.

Podesta's attack attracted the attention of another top Democratic operative, David Axelrod. "Shootout at Ft. Des Moines corral? As caucuses approach, Team @HillaryClinton has @SenSanders within their sights," the former Obama campaign strategist tweeted.

Gun regulation has become a hot button issue after President Obama issued executive orders requiring people engaged in selling guns as a business conduct background checks on all firearm buyers.

Clinton and former Maryland Gov. Martin O'Malley have called for more stringent background checks for gun purchases. Sanders has been less vocal on the issue, though he supports Obama's executive actions.

Sanders' home state of Vermont is mostly rural and gun-friendly, a reason he has been relatively muted on gun control.

Podesta's attack came after Sanders campaign manager Jeff Weaver told reporters in a Friday afternoon conference call that there is "zero daylight" between Obama and Sanders on guns.

That's "just not true," Podesta said during his own phone call with reporters. "Democrats have a real choice because standing up to the gun lobby is a real difference between Sen. Sanders and Hillary Clinton."

Clinton told MSNBC's Chris Matthews Friday that Sanders should admit he erred by voting against the Brady Bill, which required background checks for gun purchases.

She ripped him for backing what she called the "Charleston Loophole," an amendment to the Brady Bill that allows a firearms dealer to sell a gun if the FBI doesn't complete a background check within three days. The monikor attempts to link the amendment to the murder of nine in a Bible-study group last year in Charleston, S.C. Alleged shooter Dylann Roof bought the gun used in the shooting after a background check failed to catch his criminal record.

"When it really mattered, Senator Sanders voted with the gun lobby and I voted against the gun lobby," Clinton said. "Maybe it's time for Senator Sanders to stand up and say, 'I got this one wrong.'"

Sanders' Twitter account shot back at Clinton. "Maybe Hillary Clinton should apologize for this?", the campaign tweeted, with an image of a message sent from Hillary Clinton's 2008 campaign to supporters that attacked Obama's record on access to guns.