How Jewish did you have to be before the SS made you wear a yellow star on your coat whenever you went out in public? Surely we have a role model we can look to for answering these sorts of difficult questions. We're not reinventing the wheel here.
One Jewish grandparent, or even a zero amount of Jewish blood if you considered yourself Jewish. For example, if your mother's mother's mother's mother... etc was Jewish, technically you are, but most would have lost that particular leaf of culture amongst all the tangled branches of the family tree. In practice, this meant that some devout Christians ended up in the camps; if your paternal grandfather was Jewish and had married a Christian, she generally didn't convert, so their son would be Christian by default, and he'd generally marry a Christian, too.
But they also had categories, so for example if you'd converted from Judaism to Christianity before the race laws came about, or if you were Christian but married a Jew, you'd be a "second degree mischling". You can read about it here -
https://en.wikipedia.org/wiki/Mischling_Test.
You needed to have a family tree back to 1750 free of Jews, Poles, Africans and so on to get a German Blood Certificate which let you join Zer Partee and the SS. There were quite a few Generals and so on who had some Jewish or Polish or whatever blood whom Corporal Schicklgruber issued a German Blood Certificate so they could keep working for the state. Anyone who's ever researched their own family tree will know that we're basically all mongrels, we've got all sorts of heritages if we go back far enough, especially once you factor in the people of doubtful parentage, like Hitler's father.
The full Jews went to the camps first, the first degree mischlings next, and the second-degrees later. I suspect that had the regime continued, eventually all of them would have been killed, including Generals with Slovenian heritage and so on. And certainly they would have returned to their original victims: the severely disabled, whom they first started murdering as early as 1934 ("for their own good!") but they had to stop under public pressure - I've no doubt they would have killed disabled war veterans after any victory. I mean, as the Red Army approached Berlin Hitler ordered that everything be destroyed, and that the German people had failed him and all deserved to die, etc. While obviously racism was a primary motive, in the end the Nazis wanted to kill everyone, including other Nazis.
Interestingly, the test for being Jewish enough to qualify for Israeli citizenship is more strict than the test the Nazis applied. So for example if your father was Jewish and your mother wasn't, you'd be in the camps, but Israel won't take you as a citizen; if your father were alive he could make aliyah and then convert you as a child, but if he died before you wanted to go to Israel you'd miss out. So that had Israel with its current laws existed in 1935 and the Germans allowed free migration to it, a significant number of people still would have died in Treblinka and so on.
Which is all very interesting, but I don't think Blood Certificates are coming to the US any time soon. Remember when Obama was going to send black helicopters to FEMA camps guarded by UN soldiers? Americans have a tendency to hysteria, and to assume any adverse event will lead to dictatorial Armageddon. More likely, Drumpf is just mouthing off once again, and it'll be forgotten in a week or two; less likely, he's actually pushing his powers to see what he can get away with. "The Supreme Court has made their ruling, now let them enforce it," kind of thing.