Let's not forget that the demographic explosion of minorities skews heavily young and thus more likely to be Democratic. Minority births reached a majority in 2011 , and around 55-60% of today's under 18 group is minority. It is projected that the under 18 cohort will reach minority majority status later this decade.
The young vote will be skewing even more black and brown each election cycle , furthering their Democratic lean.
Unless the Republicans actually ... *gasp* ... reach out to minorities.
They won't. It's much easier for them to become the white party.