Diamond is a senior vice-president at Realty Capital International, a real estate investment banking firm, and a former vice-president at Bear Stearns. Prior to his career in finance, he served in the U.S. Navy and was the Navy's legislative liasion to the House of Representatives. A Truman Security Fellow, he also serves as vice-chairman of the Democratic National Committee's Veterans and Military Families Council.

According to a Times story about his 2004 wedding, Diamond's mother served as the district director to former Staten Island Republican Congressman Vito Fossella.

Grimm was a political novice when he eked out a win 2010 against one-term Democrat Mike McMahon. The district covers parts of Brooklyn and all of Staten Island, and has voted heavily Republican in presidential elections over the last several cycles, but is likely to become more Democratic after the most recent round of redistricting, and is seen  as the quintessential New York City swing district

McMahon has been hinting that he will run himself, but has made no moves yet to put together a campaign.

Grimm has come under fire in recent weeks for his full-throated endorsement of Paul Ryan's budget, even though cuts in that proposal could hurt seniors.

A phone call to Diamond was not returned.