AN OATH OF CITIZENSHIP should be required in order to vote:

I, [_ name _], do solemnly swear that I support and defend the Constitution of the United States against all enemies, foreign and domestic, and that I bear true faith and allegiance to the same. So help me God.

Those who have (or had) a military service background will recognize the origin of the oath.

The post from which I took the idea is on another topic, but no good idea should go unpublicized.