Israel flew F-35s all over S-400 covered territory in Syria.
I don’t have any links. From what I read, detection of stealth aircraft is achievable, but locking on with missile guidance is not — they use two different systems with different frequencies for those two activities.
I also read that the U.S. was able to acquire an S-400 battery to study.
“Israel flew F-35s all over S-400 covered territory in Syria.”
Except that they had agreement with Russia (and possibly Syria). That agreement is likely the main reason that they won’t help Ukraine, even given the threats from the US - Israel needs to prevent Iran (or its allies) from establishing a beachhead in Syria.
Also, in the 1982 War in Lebanon, Israel was able to take out S-200s, but when they were manned by Russians, it came at the cost of Israeli planes being shot down.
We really don’t know what will happen with direct engagement with S-400s, and if it doesn’t go well, then what does that say to the rest of the world regarding our ability to project power? That’s why I don’t think we’ll risk it.