  In an EHT study of a Jy-level target, Safarzadeh et al. (2019) show how
astrometric monitoring could constrain massive black hole binaries with the
wide separations that make them long-lived against gravitational wave losses,
and with the small mass ratios expected from merged satellite galaxies. With
this ngVLA study, we show how such frontier topics could be explored for the
more numerous mJy-level targets, such as NGC\,4472. We also discuss how ngVLA
astrometric monitoring could test the upper limits from pulsar timing arrays on
gravitational waves from NGC\,4472.
