Is social media a part of a background investigation?

As of 2016, federal agencies were authorized to and do now collect, use, and retain publicly available social media information for Personnel Security Background Investigations and Adjudications.  Subsequent to recent well-publicized events, DoD has been taking a more aggressive approach to monitoring social media posts by Service members, perhaps flagging "inappropriate" social media content similar to flags for financial trouble, criminal arrests or drug/alcohol problems.