I saw a post in /r/historyporn showing Einstein posing for a sculpture of himself. It stated that he did that while in hiding from the Nazis in 1933. I asked a question about that and was told I might get an answer here.
If Einstein was hiding from the Nazis in 1933, evidently they already knew how valuable he was to any scientific efforts or research they may have had planned. Therefore, one could assume they would also want him to stay out of the hands of their enemies or potential adversaries. Once he was out of Germany, and working and living elsewhere, there are countless photos of him enjoying life as just another celebrity or VIP in the scientific world - out in public without any visible security measures. Were there ever any attempts or plots by the Nazis to capture or kill him to keep him from aiding the Allies? Did he have a security element that watched over him?
Einstein feared that there were those who might want to assassinate him as early as the 1920s. He was an outspoken enemy of right-wing and militaristic elements in Germany, a prominent and world-famous scientist, and a Jew. He was deeply affected by the assassination of German foreign minister Walther Rathenau in 1922.
My recollection — though I am trying to remember where I read this — is that Einstein did learn there were people arrested under the charges of conspiring to assassinate him at some point. But it never went anywhere.
The reason that Einstein was a target was not because anyone thought his science was valuable. It was because he was a very famous person who lent his voice to strong political positions. This made him enemies in many places (including the USA, where the FBI pursued him doggedly for his advocacy of radical positions like Civil Rights and racial equality). Einstein himself had essentially no "value" other than his fame at that point.