It doesn't matter what those Christians may say, it matters what the Bible says. The Bible is the written word of God, and God is the final authority in a Christian's life.

in Genesis 12, God says to Abraham "I will make of you a great nation". He says "I will bless those who bless you, and him who dishonors you I will curse".

In Galatians 3:29, Paul reveals that "if you are Christ's, then you are Abraham's offspring and heirs according to the promise [that God gave Abraham]"

In John 15, Jesus says "“I am the true vine, and My Father is the keeper of the vineyard. He cuts off every branch in Me that bears no fruit, and every branch that does bear fruit, He prunes to make it even more fruitful."

In Romans 11, Paul reveals that while some Jews did believe in Jesus, the branches of unbelieving Israelites were broken off from the vine and gentiles that believe have been grafted into that vine.

And lastly, 1 John 2:23:

"Whoever denies the Son does not have the Father, but whoever confesses the Son has the Father as well."

In the end-times, the remnant of the Jews will come to acknowledge Jesus as their Lord and be saved (Romans 11:25-27). However, it seems compelling throughout the New Testament that Christians are in no way shackled to supporting Judaism nor the current government and state of Israel.

If you want more information on this topic, see https://youtu.be/glqMDrA1dE8, https://youtu.be/W7Fl14sgzWw