I am not sure if a person holding dual citizenship can represent United States in other nations.Normally Jews or people born in other nations may hold dual citizenship as many countries unilaterally allow their citizens to become American Citizen without loosing their citizenship.
When one becomes citizen of United states one has to take the following oath
I hereby declare, on oath, that I absolutely and entirely renounce and abjure all allegiance and fidelity to any foreign prince, potentate, state, or sovereignty of whom or which I have heretofore been a subject or citizen; that I will support and defend the Constitution and laws of the United States of America against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I will bear arms on behalf of the United States when required by the law; that I will perform noncombatant service in the Armed Forces of the United States when required by the law; that I will perform work of national importance under civilian direction when required by the law; and that I take this obligation freely without any mental reservation or purpose of evasion; so help me God.
Oath of allegiance has a long tradition ,first such recorded oath was taken in may 30th, 1778 at valley forge during the revolutionery war.
Michael Borenstein now Michael B Oren has lived his adult life in Israel and has served in its armed forces .Naturally he associates with israel .He chooses to represent Israel, so he should not hold dual citizenship and every American representing us in other countries should not be alloweed to hold dual citizenship also.