The man depicted in the footage -- which was first published by The Daily Caller, and which has been making the rounds online since -- has been identified as 24-year-old Aidan Maese-Czeropski ... an aide to Democratic Maryland Senator Ben Cardin.

Unclear exactly when this sex tape was filmed, but TDC got its hands on it and threw it up on its site. Indeed, it shows Maese-Czeropski having anal sex with another man in a judiciary hearing room within the Hart Senate Office Building ... and reports indicate it's one where confirmations/grillings go down -- including for SCOTUS nominees, etc.

The camera is being held by the man who's doing the penetrating -- he films both Maese-Czeropski in front of him and the empty room that they're in ... capturing lots of angles.

It appears the two men are having sex where Senators themselves often sit ... perched up on the bench and looking down onto the table where witnesses/nominees would normally be.

Once the staffer in question was linked to Cardin ... a spokesman for his office confirmed the guy was no longer working for the lawmaker -- saying, "Aidan Maese-Czeropski is no longer employed by the U.S. Senate. We will have no further comment on this personnel matter."

Aidan himself appears to have also addressed the scandal -- a purported message from his since-scrubbed LinkedIn is being circulated ... and it reads in part, "This has been a difficult time for me, as I have been attacked for who I love to pursue a political agenda."

He adds, "While some of my actions in the past have shown poor judgment, I love my job and would never disrespect my workplace. Any attempts to characterize my actions otherwise are fabricated." Just about all of Aidan's social pages have now been wiped.