@Miller,
Interesting topic. Some relevant observations:
* Romney won a large percentage of Whites who voted, but White voter turnout was low.
* Blacks voters, by contrast, had historically high participation rates in the 2008 and 2012 presidential elections.
* Romney won 27 percent of the Hispanic popular vote, nationally, in 2012.
* Presidential elections aren't determined by the popular vote, but by the electoral college. Obama barely squeaked by in 2012 where the popular vote is concerned, winning just 51.06% nationally; but he won the electoral college vote by a landslide, 332 to 206.
* Electoral college votes are determined by statewide popular vote results. Most states are solidly Republican or Democrat in their federal politics. That means a few extra Hispanic votes won't make much difference in most states, everything else remaining equal. Only in states "purple" enough to involve a close to balanced mixture of Democratic and Republican voters, will a marginal group like Hispanic voters make a critical difference. These "swing" states include Florida, Nevada, Colorado, and Virginia.
* Factors in ethnic voting, from least to most important: how many in each group (White, Hispanic, etc.); how many voting age in each group; how many citizens (native or naturalized) of voting age in each group (federal elections exclude permanent resident non-citizens); how many in each group are registered to vote; how many registered voters in each group actually vote in an election.
As of 2015, according to the Census Bureau, of citizens 18 or older:
154 million Whites
27 million Blacks
25 million Hispanics
9 million Asians
5 million Other
But Hispanics have lower turnout rates than Whites and Blacks (i.e. smaller percentages actually vote).
Somehow I don't think that Black voters will turn out as enthusiastically for Hillary Clinton as for Obama.
Hispanic voters were mobilized by immigration issues in Obama's elections, when he promised to change immigration law. But the Democrats didn't follow through on their promise of comprehensive immigration reform when they had control of Congress, and now they don't.
Voter turnout may be affected by two things: enthusiasm for a candidate; fear of the other candidate.
Minority groups may cancel each other out. If Blacks arw less enthusiastic about Hillary Clinton and voter turnout is less, but Hispanics hate the Republican candidate and make a point of voting against him, the result may not be as decisive as could otherwise be the case. At the same time, the demographics of swing states are more important than the national popular voting trends by ethnic group.