Define "Western".
Besides, name one Christian country these days.
In the sense of a country's dominant culture being in accordance with Christian values? America was, and hopefully will be again.
Early Americans came to get away from the anti-Israel religion of Europe. George Washington was rather friendly with early American Jewish settlements. ...Puritans and Huguenots who came with them, too.
That's odd, since you wrote of the (unfortunately) secular modern state of Israel "Why support a country defined by a religion which rejects Christ?" Judaism is in no way defined by Jesus. He was one of many false messianic claimants of no more value than Sabbatai Zvi or Jacob Frank, except in so far as Christianity has defined the West. And Israel is as much part of the West as Rome, Athens, and the US. But, it certainly is not Christian. Sadly, I would argue taht most of Europe is post-Christian. What country do you support other than Vatican City?