The United States is wracked by a spasm of anti-cosmopolitanism and fear of radical subversion. It is exemplified, for many Americans by the election and presidency of Obama himself: black, yet biracially cosmopolitan, urban, intellectual, raised partly in a Muslim country, and the abandoned son of a Kenyan activist and academic. Millions of conservatives still suspect him of being un-Christian and, literally, not a native-born American qualified to serve as president. That Obamas election occurred simultaneously with the largest economic contraction since the Great Depression exacerbated these cultural tensions.
The current conflict is a continuation of one over the past century in the United States between what the historian Gary Gerstle has called
the racial nationalism of blood and ethnic supremacy (ethno-nationalists) and a more expansive civic nationalism which promises a common political project of equal rights and respect for all. America has seen expressions of both racial and civic nationalism in its historyboth are quintessentially American articulations of political power and hierarchy. Yet these different national projects
one culturally and ethnically homogeneous, the other inclusive of differences, yet seeking to subsume them into a Party of America, in political theorist Rogers Smiths words
Obama today embodies the fears of ethno-nationalists and the (often-disappointed) hopes of civic nationalists ...
http://www.theatlantic.com/politics/archive/2015/12/the-return-of-the-1920s/422163/?google_editors_picks=true
It is not right to "blame" Obama for the rise of Trump but the election of Obama represents much of what the republican base is afraid of.