Neither.  Most likely Federal Protective Service or US Capitol Police.  He wasn't "aiming a rifle", he was "glassing" - using his scope to watch the crowd.    There is a second man behind him.  Don't if that is a spotter or an observer/commander.  I can't tell about the uniform - looks like camo or OD.  LE does use OD, very rarely camo.  HArd to tell... The active threat list would dictate the security posture.    If this is genuine LE or MIL, it wouldn't be a break in protocol.  If it were private security, there should be an issue. @zaakir1