Obama divided the country, not Trump fallacy.

There is a lot of political ideology in here, so let's get to the core of the issue, assuming this is what is happening:

Person A did X.
X Caused person B to do Y.
Therefore, Person A caused Y.

We can see where this is reasonable, and where it is problematic. Consider:

My wife ate my business report.
I couldn't present my business report, which got me fired.
My wife caused me to get fired.

or

My wife didn't have my dinner ready on time.
So I beat her with a dead fish.
It is my wife's fault she was beaten with a dead fish.

We want to know if the conclusion is justified. To answer that, we need to ask if X was really a direct cause of person B doing Y. Was Y a reasonable response? Now depending on the content of the argument, you will get different answers, and each side has to make their case. One side might call Questionable Cause fallacy or even Slippery Slope.

What fallacy is this? There are multiple fallacies within the question

Obama becomes the first black president of the U.S and tries to unite the diversity. This an attempt to include a conclusion in the factual statement of the premise.

White racists in the U.S did not like this so they voted for a white racist to divide the country again. This is clearly "petitio principii"

For this reason, whites claim Obama divided us, not Trump. Petitio principii is fallacious and no conclusion should be based on it.

It seems that the U.S became divided because of racist whites not liking a black president, and so there was a backlash response from them which divided us. There seems to be a fallacy here in that Obama, just because he was black caused them to rebel and divide. So they project their dividing actions on Obama, when Obama can not help the color of his skin or their reactions to it. But the white racists can help their dividing actions. This continuation is a weak argument, once again taking the a priori conclusion of the writer as if it were a fact.

So, who divided more? Obama or Trump? No valid conclusion can be drawn from the syllogism.

I also want to add that Obama was a democrat too and the republican party is the party of racism. It use to be the democratic party, but political realignment happened after the civil-rights movement. So, I also believe that tribalism is also a part of this equation as well. Includes non-sequiturs and mere assertions.