Mikey, would you be referring to the Jefferson Club at 77 Conklin Ave in Canarsie? That club is still there I think you can view it if you look at Google maps. It was the HQ for the Democratic leader for Brooklyn, Meade Esposito for quite a while. Apparently there were allegations of bribery, corruption, political backroom dealings, etc. made but no allegations to mob ties that I could see.

Maybe the club in the Pileggi article you read was referring to the Mangano Democrat Club, mentioned in Phillip Carlo's book Gaspipe, near Gaspipe's house on Union Street in Park Slope? According to the book it was a scene for meetings and backroom dealings between Union officials, businessmen and politicians etc. so safe to say the mob wouldn't have been very far away from any deals being made.

Here it gets a bit confusing though and maybe off topic from your original post, sorry. I found reference to a City Democratic Club in the Brooklyn Daily Eagle newspaper from October 22nd 1937. There is a V.Mangano mentioned in an article on page 7 so I assumed this is the same City Democratic Club which Vincent Mangano established in the 1930s. But this club was located at 367 Clinton Street which is obviously not a few doors up the road from Gaspipe's house.

The link to the article I found is here under the heading "City Club to Fete Democratic Slate"

http://bklyn.newspapers.com/newspage/52823463/

..it's interesting even if off topic from your original question! This all started because I was trying to figure out what was the address of the Mangano Club on Union St mentioned in Carlo's book...and despite all this research I failed, so I gave up in the end. haha..