If Obama did not fix these racial issues in 8 years, how is Trump to do it in 3?  Why didn't Obama do it?  Since he was the President?

There have always been and always will be racial issues in this country, no president is going to change that.  100 years ago people might have thought it would be a thing of the past by 2020, but 100 years from now it will likely still be an issue, human nature being what it is, and besides, democraps have no desire to see it go away, they use it for political purposes.

No president can "fix" people's attitudes. Bigotry of all kinds is learned in families, in neighborhoods, among peers, from pop culture.  American society did not seriously begin to address prejudice and racism as problems until the mid 1800s, then not again til the 1940s-today.  Some people expect revolutionary change, but people's beliefs change like glaciers.

In case you didn't notice, probably because you don't live in the U.S., Obama was a major target of "these racial issues".  The far right-wing, white supremacist Republican and Republican Tea Party members had no interest in fixing racial issues because they were too busy catering to their white racist base and spreading hate.  Conservatives have such convenient memories when it comes to such things. Google "tea party racism" +images for many more examples.

The only thing Traitor trump knows how to fix is an election.

The difference is that Trump is actually doing something about it.

Obama tried. Trump has no interest in trying. 

You overestimate the power of the President.

The reason we see this flare up is Trump has spent his run for President and his years as President marching America backwards in the opposite direction that Obama brought us in.