Not sure what our sin has to do with blasting away at a President, unless you view doing so as sin, which I do not. It is perfectly acceptable, and our command to point out sin, regardless of who it is. The Kings of Scripture have never been given a pass, nor do governing authorities today.
And that, I feel, is how God would have us "treat the President." Not overlooking sin because it fits our agenda. And that is precisely what many do.
Obama sinned by advocating ungodly and unbiblical agendas. If Trump does so as well, it is our responsibility to point that out.
But we are still under command...to pray for him. And so far I haven't really seen Trump do anything that warrants placing him in a category with Obama. I think what we are witnessing is someone who is either a babe in Christ or perhaps on the verge of being saved, and without question I feel the Lord is working in his life. As I keep saying, I will wait and see what happens.
God bless.