1. Jesus was born in human fashion, as a Jew, and had a ministry to the Jews. (Galatians 4:4)
I find this misleading. When I think of Jesus “having a ministry,” I think of him tramping about Galilee with his disciples healing and teaching. Paul doesn’t seem to be talking about anything like that: “But when the set time had fully come, God sent his Son, born of a woman, born under the law, to redeem those under the law, that we might receive adoption to sonship.” Gal. 4:4-5.
2. Jesus was referred to as "Son of God." (1 Corinthians 1:9)
This is just plain wrong. Paul doesn’t say that the historical Jesus was Jesus was referred to as “Son of God.” Paul himself refers to Jesus Christ as the son of God. "God is faithful, who has called you into fellowship with his Son, Jesus Christ our Lord." 1 Cor. 1:9. This isn’t something that Paul is indicating he knows about a historical person. This is something that Paul knows about the exalted Christ who revealed himself to Paul.
3. Jesus was a direct descendant of King David. (Romans 1:3)
Paul does say this.
4. Jesus prayed to God using the term "Abba." (Galatians 4:6)
I think this one is just plain wrong, too. Paul isn’t talking about anything the historical Jesus did. He is talking about what the spirit does in the heart of the believer. "Because you are his sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, 'Abba, Father.'” Gal. 4:6.
5. Jesus expressly forbade divorce. (1 Corinthians 7:10)
6. Jesus taught that "preachers" should be paid for their preaching. (1 Corinthians 9:14)
7. Jesus taught about the end-time. (1 Thessalonians 4:15)
My problem with all three of these is that Paul doesn't claim that the historical Jesus taught these things during his earthly ministry nor does Paul ever claim to know about anything the historical Jesus said or did during his earthly ministry. On the other hand, Paul does claim to know things by divine revelation. Why should we think that Paul saw the historical Jesus rather than divine revelation as the source of these teachings.
8. Paul refers to Peter by the name Cephas (rock), which was the name Jesus gave to him. (1 Corinthians 3:22)
The truth is being stretched here. Paul refers to a man named Peter, but he never indicates that this man had any connection with the historical Jesus.
9. Jesus had a brother named James. (Galatians 1:19)
I won't quarrel with this although Paul refers to James as “the Lord’s brother” rather than “Jesus’ brother.”
10. Jesus initiated the Lord's Supper and referred to the bread and the cup. (1 Corinthians 11:23-25)
Paul does say this, although he claims to have received this from the Lord as opposed to learning about it from anyone who knew the historical Jesus and attended the meal.
11. Jesus was betrayed on the night of the Lord's Supper. (1 Corinthians 11:23-25)
This may reflect Paul's belief, although some scholars think that “handed over” is a more accurate translation than betrayed. Once again, Paul attributes his knowledge of this to revelation.
12. Jesus' death was related to the Passover Celebration. (1 Corinthians 5:7)
I think this is misleading. Paul says that Jesus is our Passover lamb, but he doesn't link the death of the historical Jesus to the dates on the calendar when the Jews celebrated the Passover.
13. The death of Jesus was at the hands of earthly rulers. (1 Corinthians 2:8)
Paul does say this, although he doesn’t tell us who those rulers were.
14. Jesus underwent abuse and humiliation. (Romans 15:3)
This seems like another long stretch. I don't see anything in this passage to make me think that Paul is referring to anything that happened to the historical Jesus. In fact, it looks to me like he is talking about things that will happen to Christians.
We who are strong ought to bear with the failings of the weak and not to please ourselves. Each of us should please our neighbors for their good, to build them up. For even Christ did not please himself but, as it is written: “The insults of those who insult you have fallen on me.” 4 For everything that was written in the past was written to teach us, so that through the endurance taught in the Scriptures and the encouragement they provide we might have hope. Romans 15:1-4.
15. Jewish authorities were involved with Jesus' death. (1 Thessalonians 2:14-16)
More of less. Paul refers to the Jews to generally rather than the Jewish authorities and some scholars think this passage is an interpolation.
16. Jesus died by crucifixion. (2 Corinthians 13:4, et. al.)
Paul does say this.
17. Jesus was physically buried. (1 Corinthians 15:4)
Paul does say this.
According to Hannam, mythicism "is simply a bad hypothesis based on arguments from silence, special pleading, and an awful lot of wishful thinking." I think many mythicists are guilty of all these failings, but I have yet to see an attempted refutation that didn't engage in the same fallacies. I guess historicists believe in debunking fire with fire.