The Democratic Party takes the Black vote for granted and lines up with the ministers as political ambassadors, while the business of the Black community is ignored. At the same time, there is very little Black political participation with the Republicans.
If enough people vote for third party candidates, then the winner of the election can well find himself (or herself, in a future election) with less than 50 percent of the popular vote, as has happened numerous times, and therefore much less of a claim to any sort of mandate.
If the remarkable pattern of monthly Republican frontrunner changes had structural reasons, then the pattern could be repeated in the general election campaign, with potentially several minor party candidates rising in polls.
If Americans were told to choose between two cars, shirts, colors or family sizes, we'd rise up in revolt. Tell us we have only two parties, however, and we accept it as though any alternative is unimaginable.