Long Baselines for Multi-Messenger Supermassive Black Hole Science When illuminated as radio-emitting sources, binary supermassive black holes can be detected through their dual radio-emitting cores, by their large-scale jet morphologies, and/or by periodic core variability. So far, the most robust binary identification method has shown to be direct imaging of radio cores. The most massive (>~10^8 Msun) binary systems will, in the next 5+ years, also become detectable via their gravitational radiation by pulsar timing arrays like the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). We will report results from a simulation of the binary supermassive black hole population in the local (z<~2) universe for which we have included a predictor of radio emission. Thus, we have the ability to analyze the bulk statistics and properties (mass, distance, etc) of sources that will potentially be detectable by both NANOGrav and by future radio instruments like the ngVLA. Assuming that future radio instruments will aim to resolve dual radio cores, we will demonstrate how effective the ngVLA will be at probing multi-messenger targets as a function of its maximum baseline. -- T. Joseph W. Lazio Chief Scientist, Interplanetary Network Directorate Jet Propulsion Laboratory, Interplanetary Network Directorate