Sitting among the hundreds of unsigned bills on Gov. Gavin Newsom’s desk is a measure called Senate Bill 9, which would allow duplexes on lots throughout California, including neighborhoods where apartments have long been banned.

The bill was the centerpiece of this year’s legislative efforts to tackle the state’s housing and homelessness crisis, by increasing density and helping to backfill the shortage that is at the root of the state’s affordable housing problem. Economists from both parties have long advocated just such a move.