John Sampson is the favorite to replace Malcolm Smith as Democratic leader in the State Senate, enjoying the support of a growing number of his colleagues and the blessing of the Conference of Black Senators. Which means that, depending on the outcome of the ongoing struggle for control of the Senate, this anonymous official may soon be one of the Three (or four?) Men who ostensibly run the state. So, who is he? Above all, it seems, he is a consensus guy: someone who flies below the radar, and whom nobody finds particularly objectionable. A lawyer representing an eastern Brooklyn district containing Brownsville and Canarasie, Sampson was first elected to the Senate in 1996 after unseating an incumbent, Howard Babish, in a Democratic primary.