How can some evangelicals justify being anti-semitic when Jesus himself was Jewish?
It's easy. Antisemitic Christians blame the Jews for their rejection of Jesus as the fulfillment of prophecy—the Messiah. They champion Christ as a rebel against the Jewish establishment, the Sanhedrin, for which he was executed. So, while Christians identify with the Hebrew birthright, as chronicled in their Old Testament, and consider themselves as sons and daughters of Abraham, the antisemitic camp despises the Jews for their effrontery and prosperity.
Please understand this, however. Many Evangelicals find common cause with the state of Israel, under the premise that Jerusalem represents ground zero for armageddon, which these believers look forward to, per the final book of the Bible—Revelation.
There is no historical evidence that a man named Jesus Christ ever existed there are tons of historical documents written at that time and other than the Bible no one mentions him and by the way did you know that for up to a thousand years before him they've been like a dozen other people who claim the exact same thing
Matthew 27: 24 to 25 is the usual excuse
24 When Pilate saw that he could prevail nothing, but that rather a tumult was made, he took water, and washed his hands before the multitude, saying, I am innocent of the blood of this just person: see ye to it. 25 Then answered all the people, and said, His blood be on us, and on our children.