This'd be a whole barrel of fish. If Jesus came back, how could you tell it was Jesus and not just some new David Koresh or Charles Manson, the bible doesn't even give a metric for it and gives examples of unholy people committing miracles so that's out.
Besides, assuming the Christian bible as wholly true (which is necessary for this post), the guy claiming to be Jesus and running for world leader is supposed to be the anti-christ, so by reading the posts here the Christian's are nearly unanimously supporting the beast while the non/differently believing secularists are the last bastion against Satan.
Beyond this, democracy trumps theocracy, so assuming it is not a fake or the anti-christ, he would still dictate from a position of the Kingdom of God, there just isn't the freedom necessary for a democracy in this. God has a plan for each person sounds a lot like Commie speak for forced labor assignments, well as does the requirement to disown personal wealth, the hardliner stance against committing the same sin twice (read the book of Hebrews, after the gospels, before revelations...I know "the boring stuff" God looks kinder upon those who blatantly reject his way than those who sin after learning not to), it would pretty much be an impossibility to live up to these standards and maintain personal freedom.
Sure that personal freedom I'm talking about is largely selfishly using personal wealth, committing various sins of the flesh, not tithing, or not bowing to an abstract authority figure, etc. that'll all send me to hell according to the good book, but as a US Citizen, that's my temporal right.