“Career Politician Ed MarkeyEdward (Ed) John MarkeyDem senators demand Trump explain ties to Koch brothers Overnight Cybersecurity: Senators want info on 'stingray' surveillance in DC | Bills to secure energy infrastructure advance | GOP lawmaker offers cyber deterrence bill Overnight Tech: Alleged robocall kingpin testifies before Congress | What lawmakers learned | Push for new robocall rules | Facebook changes privacy settings ahead of new data law | Time Warner CEO defends AT&T merger at trial MORE has started his campaign with a textbook despicable political attack to attempt to connect me with Osama Bin Laden in the minds of voters," Gomez said. "This attack is an insult to my service and an insult to the intelligence of the people of Massachusetts. Congressman Markey should direct his campaign to immediately stop this ad, stop his mudslinging and debate me on issues that Massachusetts voters care about, the economy and jobs.”

But Markey's campaign says Gomez is complaining about the Massachusetts congressman featuring a video the Republican nominee created himself — and demanding Gomez apologize to President Obama.

"Before he was a candidate for Senate, Gabriel Gomez was a spokesman for a secretly-funded special interest group that spent half a million dollars during the 2012 election attacking President Obama over the killing of Osama bin Laden," said Markey campaign spokesman Andrew Zucker in a statement. "Now Gabriel Gomez is trying to distract from the fact that he attacked the President of the United States over the death of bin Laden by attacking Ed Markey…. For leveling such baseless charges, Gabriel Gomez owes President Obama an apology."

The web video in question highlights Gomez's work for a special interest group called the Special Operations OPSEC Education Fund that filmed a video during the 2012 campaign accusing President Obama of politicizing bin Laden's death.

Markey's ad features Gomez defending OPSEC on MSNBC, and then a clip of the video produced by the group that accuses President Obama of "politically capitalizing on U.S. national security operations and secrets."

That video clip, originally produced by OPSEC, includes images of both President Obama and bin Laden. Because it is shown next to an image of Gomez, the Republican Senate candidate and the terrorist leader appear on screen next to each other for about eight seconds.

National Republican Senatorial Committee communications Brad Dayspring suggested on Twitter Friday that the juxtaposition was intentional, accusing Markey of going "ugly early." In subsequent tweets Saturday afternoon, Dayspring dismissed the Markey campaign's argument that it was Gomez who first politicized Bin Laden.

"Simple question for Ed Markey: Is it appropriate or disgraceful for your ad to feature a Navy veteran split screen with Osama Bin Laden?" Dayspring wrote.

The Markey campaign maintained their web ad was intended to show that Gomez isn't above partisan attacks. The Massachusetts Republican has attempted to position himself as a moderate in his Senate campaign.

"Gabriel Gomez says he is 'a new kind of Republican,' but less than a year ago he was a spokesman for a right-wing, secretly–funded special interest group that tried to 'swift boat' President Obama’s handling of the killing of Osama bin Laden," the Markey campaign said in the release.

The controversy is likely the first of many in what is shaping up to be a hard-fought Senate race. A pair of polls released this week show that Gomez is within single digits of the 20-term congressman, despite more than 60 percent of Massachusetts voters backing President Obama over the state's former Republican governor, Mitt Romney, in 2012.

--This report was originally published at 12:28 p.m. and last updated at 3:23 p.m.