Neither Trump nor President Obama are responsible, though Trump certainly bears responsibility for exploiting the resentment and anger for personal gain. President Obama was a shock to the senses of many of the relatively dormant racists in the country who for the first time, had to look up at a leader who did not look like them. President Obama did nothing to stoke any anger. It was his mere existence that stirred up the resentment, and of course opportunists like Trump, exploited that, and the GOP went along with it.
Back to my initial point. Racial and economic anxieties have gone hand in hand in this country, mainly because rather than looking at the small group of wealthy people who own most of the country's riches, people have allowed themselves to be lead to believe that lazy people of color either mooch off of their hard earned dollars, or these same lazy people of color have stolen their jobs by agreeing to work harder for less money. This resentment has been present since the beginning of the country when Irish, Indian(natives), Chinese, Mexicans, Poles, or whatever other hated group of the day was excluded from full participation in society. When Black people were taken from slavery to Jim Crow, to mass incarceration and many other policies which kept them from being part of society and where their attempts to create a thriving economy for themselves (Tulsa) were literally destroyed.
The people of this country have never come to terms with the racism that this country was founded upon. We look at it, we discuss it, but we ignore the legacy and often satisfy ourselves that "things are getting better".
So my answer would be to acknowledge that Trump has actively stoked racial tensions while President Obama was careful to always be cognizant and respectful, but the anger and hatred has been brewing in certain parts of the population for a long time.
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