Watch the First Campaign Ad to Invoke the Newtown Shootings

Locked in a close Massachusetts Senate race, Ed Markey goes negative against Gabriel Gomez.

In the first campaign ad to explicitly mention the Sandy Hook Elementary School shootings, Massachusetts Democratic Senate candidate Ed Markey on Thursday accused Republican opponent Gabriel Gomez of opposing the kind of gun-control measures that could have prevented the mass shootings that killed 26 people in Connecticut earlier this year.

"Gomez is against banning high-capacity magazines, like the one used in the Newtown school shooting," says the ad, which also mentions his opposition to an assault-weapons ban. It includes footage of Gomez explaining his opposition to both.

The 30-second spot is an early significant test of the potency of gun-control politics. Markey is locked in a tougher-than-expected contest against the relatively unknown Gomez, a former Navy SEAL, in one of the most solidly Democratic states in the country. His decision to go negative early suggests the campaign believes the race is competitive. The June 25 election will determine the successor to former Sen. John Kerry, who was appointed as President Obama's secretary of State.

Although a measure to expand gun-sale background checks failed to gain a 60-vote supermajority in the Senate last month, gun violence remains a potentially potent issue in Massachusetts. Like former Republican Sen. Scott Brown before him, Gomez's success depends on his ability to define his independence from the national GOP--a strategy threatened by tying him to the GOP's opposition to gun-control measures.

Gomez and national Republicans said they were outraged by the implication that Gomez was to blame for the Newtown murders.

"Ed Markey first compared Gabriel Gomez, former Navy SEAL and father of four children, to Osama bin Laden, and now Markey is blaming him for horrific murders in Newtown," said Brad Dayspring, a spokesman for the National Republican Senatorial Committee. "It's disgusting, deplorable, and desperate, but that's par for the course for Ed Markey, who will do just about anything to avoid talking about the issues that voters care about."