incumbent on - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Also, incumbent upon. Imposed as an obligation or duty on, obligatory for. For example, He felt it was incumbent on us all to help the homeless. [Mid-1500s]