I have explained before on numerous occasions the problems which the proclamation of Jesus as a crucified messiah present for mythicism. Let me try to restate the point again briefly, as I sought to do in a comment on another post:
The claim of Christians is that Jesus was the anointed one descended from David. In other words, they viewed him as the one who would restore the line of David to the throne.
Jesus failed to do so, at least in the manner expected.
It is unlikely that Christians would have invented a Messiah that they wanted their fellow Jews to accept, yet who was a failure.
Some mythicists claim that dying before restoring the Davidic dynasty to the throne was not failure, because there was an expectation that the messiah would die. They often point to Isaiah 53 as evidence of this.
Targum Jonathan illustrates the problem with this. It is the one example of possibly pre-Christian Jewish interpretation of Isaiah 53 in messianic terms, and it accomplishes this by making it the enemies of the messiah who suffer.