The US Constitution not only recognizes them formally as entities, unlike any other nation, but gives them the power to define their citizens. And that's where American ignorance really kicks in.
To call yourself a Native American in the US, and tag and otherwise checkboxes and represent yourself as a 'person of color' as a Native American, yes, you actually need to be a citizen of that nation.
Let's take Liz 'Wilma Mankiller' Warren for example, well published, titled, even tagged ... by her own admission, and finally her own, real 'apology' after 7 years of the US Mass and Social Media 'apologizing' for all her formal, yes, formal documentation, publications and other things stating she was a 'woman of color' and 'Cherokee' ... not just the 'ancestry' claim ...
In the US, by both Constitution and Treaty, you cannot call yourself, say, Cherokee, like you can, say, Irish. It will get you in trouble with the State Department when the Tribes force it, as the 3 recognized Tribes of the Cherokee finally did. It took 'Wilma' there 7 years, but finally she 'woke up' to how wrong she was ... even if the US Mass and Social Media is still apologizing for her, and utterly being the staple 'Ignorance of the White Man.'
I'm glad she did. I wish it wouldn't have taken letters to the State Department, as well as a letter of over 200 tribal leaders, to get her to actually meet with them after 7 years, instead of just getting her 'facts' from the US Media 'echo chamber.' But she did.