The final arbiter of what counts as 'legitimate' in the US is what's spelled out in the Consitutition, assuming the government and military are willing to enfor

The final arbiter of what counts as 'legitimate' in the US is what's spelled out in the Consitutition, assuming the government and military are willing to enforce what's written. There are some extreme scenarios where that would no longer apply, but passing readers will get the point without needing to read every possible corner case.