Same-sex marriage legislation may have reached its apogee Monday with the Senate Judiciary Committee’s razor-thin approval, but passage of the bill by the full Senate on Thursday is highly doubtful, Trenton observers say.

Twenty-one votes are needed for passage in the upper house, which Democrats control 22-18, and at least three Democrats — Paul Sarlo of Bergen, John Girgenti of Passaic and Ronald Rice of Essex County — have said they will vote against it. Only one Republican, William Baroni of Mercer County, publicly supports the measure.