No, God is not the only one who knows what is in men's souls. God is the only One to know
everything within a man's soul.
It is very easy for someone to know something of another's soul, especially when that other soul has done horrible things in public, and espoused views that cause grave harm to the weakest and most defenseless.
Knowing a person's personal and public history is one thing.
I might know that John Doe cheated on his taxes one year.
I might know that John Doe saved a drowning man.
I might know many many things about them. But knowing what is in their soul is the ability of God alone.
If you don't like Rudy for his politics that's fine. But don't try to kick God off his throne so that Siobhan can sit there to pass judgment.