(LPR - Lawful Permanent Resident, or green card holder). (LPR - Законный постоянный житель или владелец грин-карты). This is what is...

1. You send your N400 application for citizenship; 2. You get the 1st USCIS notice 2-4 weeks later about your application being accepted...

Beginning October 2020, you will need your REAL ID when you go to any Federal buildings. USCIS Field Offices are one of those.

This picture gives you pretty good ideas why: