He was the most famous (I think) disproof of “Jewish science.”
If I had been a Nazi, it would have made sense to make a special demonstration with him.
Einstein was getting toward the end of his career in the 1930’s (he was 60 in 1939). AFAIK he wasn’t even directly involved in the Manhattan Project. He endorsed it with a letter to Roosevelt and that’s about it.
It seems like there were other bigger targets the Nazis could have gone after before the war started. Especially Churchill and Roosevelt.
Had Einstein been in Europe, he probably would have been sent to an extermination camp like other Jews, Gypsies, & Gays. Lots of other scientists were. So you could say that the “Final Solution” was an assassination plan for him.
But the Nazi’s had no special reason to assassinate him.
After all, Hitler didn’t believe in relativity or nuclear science (‘Jewish Science’), so they thought Einstein was useful in keeping the USA spending vast amounts of effort on something that the Nazi’s were sure was not going to work. Anything or anyone who distracts your enemies into wasting valuable resources is something you like!
Interesting the O.S.S. (forerunner to the CIA) considered assassinating Einstein’s counterpart in Germany. Walter Heisenberg. They dispatched Moe Berg, a former baseball player who “could speak 10 languages but hit in none” to Zurich in December 1944. Berg was to determine if Heisenberg was close and kill him if he was. I guess someone in the FDR administration figured that Heisenberg was going to tell a bunch of scientists in neutral Switzerland not to go to London without taking plenty of iodine and a lead suit. wiki doesn’t mention it but apparently Berg followed Heisenberg and asked him a bunch of questions . Heisenberg thought he was being bothered by some nosy nerd and not his potential murderer. Berg decided Germany wasn’t close and let him live.
That’s Werner Heisenberg. Just to clear up any uncertainty.
Maybe they knew where he was at any time but not his name… 
If they couldn’t simultaneously know his velocity and his position he would have been very hard to assassinate.
There must have been some small chance that the assassin would think they were close to the bomb and thus assassinate him. So integrating the Quantum theory of Mind here, from outside the lecture hall Heisenberg was technically partially dead 
I would imagine assets in the USA capable of assassinating someone were valuable enough they would not be wasted on a university professor. There’s no evidence that the Nazis knew enough to consider him or any other physicist worth targetting. If they did, why not go after someone more useful like Fermi or Oppenheimer.
I am not aware that Hitler ever targeted people in other countries (outside his control) simply for ideological reasons. They were in the middle of a war, and wasting valuable intelligence assets was not productive. Besides, what would an assassination prove, other than that the Nazis did not like the target - already public knowledge.
Nazi thugs threatened Einstein and the SA broke into his house and vandalized it. He left Germany because of it.
There was no specific plan to kill him, but the SA probably would have continued to threaten him and maybe cause a fatal “accident.” And, of course, eventually he would have been sent to an extermination camp.
Once he left Germany, they didn’t care.
This is the kind of thing I was thinking of. Should’ve said “proto-Nazis.”
I forgot to say: thanks to all.
Nitpick: The SA were Nazis, not proto-Nazis.
The Nazis had very curious views on science. This was weird, because Germany had some of the finest universities in the world. Of course, the Theory of Relativity was suspect (because it had been formlated by Einstein, a jew). But quantm mechanics was also suspect-one wonders if Hitler shot himself in the foot by exiling so many capable (jewish) physicists. Heisenburg must have ahd problems with the “Jewish Science” thing-especially as Hahan and Steisman (the scientists who first provoduced nuclear fission) were both Jews.
Because of these associations, the Nazis resurrected Phillipe Lienard (as science guru)-a man whose contributions to physics ended in about 1900.
I could swear I learned that Einstein was on a German hit list - not because of the work he was doing in particular, but because he was a high profile Jew who fled to America.
I can’t remember where I heard that. I think it might have been a profile episode of Astronomy Cast.
I also seem to remember something about him refusing protection despite this.
Been watching too much “Breaking Bad”, probably. 
I wonder if he could have been on The Black Book of people to be arrested if the Nazis had successfully invaded Britain – many of the 2500 notable people on the list were not actually in Britain or were dead. Would be easier to capture him if you control the ground!
<nitpick>That’s Hahn, Meitner, and Straßmann, only one of whom was Jewish.</nitpick>
Of course, though no one in Germany knew at the time. The German-Jewish scientists whose expulsion actually doomed the Nazi’s atomic bomb program were Otto Frisch and Rudolf Peierls. They made the first calculation that showed that only a relatively small amount of fissionable material was needed to produce critical mass, and passed this on in secret to the British Government.
The Germans never repeated this discovery, when Heisenberg and the other German scientists heard about Hiroshima (they were in Allied custody at the time, and being secretly recorded), they were still talking about how the allies managed to transport tons of fissionable material.
There were plenty of other reasons why the Nazis never made a bomb, but the lack of this knowledge doomed their program from the start.
Of course, after the fact, Heisenberg claimed that he was actively sabotaging the project from the inside. If true, it was a truly heroic sacrifice, since he can’t even be glorified by history for it.