The whole issue revolves around whether someone believes that Israel is a legitimate sovereign nation or not. Jerusalem has always been Israel’s capital whenever there was a recognized Jewish nation in the land, including following the Babylonian captivity and during the Roman period at the time of Jesus and the apostles. Jerusalem was never declared the capital of any other country when controlling the land: not during the long Islamic occupation and the Ottoman Empire, and not during the years that Jordan and Palestinians controlled what is East Jerusalem from Israel’s independence in 1948 to the Six-Day War in 1967. The heartbeat of Jewish people everywhere throughout the generations of exile has been, “Next year in Jerusalem!”.
If someone — whether Christian, Jewish, or other — accepts Israel as legitimate under international Law (Balfour Declaration in 1917, San Remo Conference in 1920, League of Nations in 1922, United Nations in 1947) — then Jerusalem as the capital should not be so difficult. If for religious and other expediencies some one or some nation chooses to “trample Jerusalem under foot until the time of the Gentiles is fulfilled”, then they are more likely to avoid the obvious reality. For those who believe that the Lord Jesus Christ is going to return from Heaven to the earthly Jerusalem and establish God’s Kingdom on Earth, then even more so should we be able to acknowledge the capital of Israel which King David founded at the Lord’s leading and revelation. While present Jerusalem may have the spirit of Sodom and Egypt (Rev 11:8), it is nonetheless destined to be the city of the great King to which all nations must go up during the Feast of Tabernacles to worship Him.