I suggest you read Dick Morris's book Armegeddon. He disagrees with your take. He says that the white voter turnout was disappointingly low while black and other minority voters came out in record numbers to support Zero. IIRC, Morris said that about 10 million whites stayed home, and Trump's opportunity would be to get these whites out in 2016. (The book was published this past June.) Morris was pretty close to what eventually happened.
So Romney’s extra million votes were from blacks and other minorities?
White voters who stayed home in 2012 were overwhelmingly Democrats. That much is clear. Trump picked up an extra million GOP votes over 2012. Were they disproportionately from minorities, indicating whites were not enthused?