I think you have to kind of look at it on two levels.
There is anti-Semitism within parts of the population. This is a historic constant in Europe, it just goes through major rises and falls. Right now it's on the rise again.
The question is, how does the political sector deal with these sentiments? This is the really frightening part, to me, because it is so easy for political leaders (and wannabe leaders) to exploit anti-Semitism (and Islamophobia) for their own ends -- and, it is easier for politicians to do nothing rather than confront unpleasant populism.
There are reports that some right-wing parties in Europe are receiving support (including financial support) from Russia, which would be a very clever move on the part of Putin, but is also a disturbing development.
Obviously what's going on in Gaza is relevant, because people are using it to justify their violence and hatred. But I think it's naive to think it's the sole driver, or to think 'if only Israel behaved itself, Jews in Europe wouldn't have to worry'.