Hi Paul -
Thanks for asking your questions and welcome to the GeoNet community! I wanted to let you know that we're moving your question to the https://community.esri.com/community/gis/web-gis/arcgisonline?sr=search&searchId=7e083b15-0a91-46cc-... space so our Esri and user subject matter experts can further help answer this and future questions. So you're aware on how and where to post your questions, here's a few quick tips and reminders:
Thanks again for contributing and I hope this helps and let us know if you have any questions.
Hi Paul,
I'd suggest checking the terms of use with Bing to see if this is available under their terms of use. There are no built in capabilities through web maps to support off-line basemaps with Bing.
-Kelly