It's more of a gray area than most realize
Case in point: Guy is arrested and charged with MCDV - domestic assault, or domestic battery. The charge is amended to something like disturbing the peace.
Feds now look at the disturbing the peace charge to determine whether it included any component of violence, whether there was a "victim," and whether the "victim" was a domestic partner.
If the answer is unclear, or they have time to dig further, they go back to the original charging documents, and have been documented to have sought and obtained police reports and 911 recordings.
If the Feds determine that a MCDV has occurred, even though the guy was not specifically convicted of "domestic assault" or "domestic battery," based on what they found, they deem him a prohibited person - and it's been upheld in federal court challenges to the practice.
So it really is difficult to tell whether someone is a prohibited person in some cases.
I drink, therefore I am.