A critic of GOP US Senate hopeful Bruce Blakeman and his supporters is circulating this Web video, which questions the former Long Island lawmaker’s support by powerbroker Alfonse D’Amato, who some believe is double-dealing by also quietly backing Blakeman’s Democratic target: Sen. Kirsten Gillibrand.

D’Amato, a former Republican US senator-turned-lobbyist, was on hand both for Blakeman’s campaign announcement back in January and Gov. David Paterson’s formal selection of Gillibrand to replace Hillary Clinton last year.

(The fact that D’Amato, a longtime friend of Gillibrand’s father, lobbyist Doug Rutnik, was standing front-and-center on stage and closer to the newly-minted Democratic senator caused quite the buzz at that press conference).

POLITICO’s Glenn Thrush suggested not long ago that D’Amato’s backing of Blakeman “only further proves” the ex-senator is trying to help Gillibrand because Blakeman isn’t viewed as a strong challenger, even though he has amassed the most GOP support of her three would-be challengers to date.

There’s no name on the (lengthy) e-mail that accompanied the video, but the format looks a lot like one used by an advocate helping one of Blakeman’s primary opponents, former Rep. Joe DioGuardi.