On the one hand, U.S. Senate hopefuls Gabriel Gomez and Edward Markey seem to be making compromises with each other regarding, for instance, whether to have another debate and releasing tax returns.

On the other hand, the campaign to succeed former Sen. John Kerry, a Democrat, in the Senate is getting nastier.

In a recent interview with National Public Radio, Gomez, a Republican, referred to his opponent, a Democrat and long-time congressman, as “pond scum.”

"...For him to be as dirty and low, pond scum, like to put me up next to bin Laden, he’s just gotta be called what he is. It’s that simple.”

- Gabriel Gomez

That followed a new Gomez campaign ad assailing Markey for his recent campaign video showing Gomez’s face next to that of Osama bin Laden and saying that Gomez does not want to ban high-capacity magazines "like the ones used in the Newtown school shooting."

In the NPR interview, Gomez responding to Markey’s ad attacking him.

“I don’t think there’s anything more offensive,” Gomez said. “You know I’ve got four young kids, and they gotta sit there and gotta see an ad with their dad — who served honorably, talk to anybody I served with — whether as a pilot or as a SEAL, anybody I worked with. And for him to be as dirty and low, pond scum, like to put me up next to bin Laden, he’s just gotta be called what he is. It’s that simple.”

Meanwhile, Markey has agreed to release several years of his tax returns.

A spokesman for Markey said he will release the returns on Friday going back to 2005. That's more than Gomez, who released several years of tax returns during the Republican primary.

Gomez and state Republican leaders had ramped up pressure on Markey to release his returns.

Also, Markey and Gomez have agreed to another televised debate in their race for the state's special U.S. Senate election.

The June 18 debate is being sponsored by a Boston media consortium.

The two candidates have already agreed to a televised June 5 debate sponsored by WBZ-TV and The Boston Globe.

Both candidates have said they want at least three debates, but have wrangled over the details.

The special senate election is June 25.

The Associated Press contributed to this report.

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