If you’re a political junkie — or at least if you’re a conservative political junkie — you’ve probably seen the map. It’s a map of the United States showing the congressional districts won by Republicans in red and those won by Democrats in blue.

It looks almost entirely red, except for some pinpoints of blue in major metropolitan areas and a few blue blotches here and there — in Minnesota, northern New Mexico and Arizona, western New England, along the Pacific Coast.

Of course it’s misleading. Congressional districts are of basically equal population, and Democrats tend to roll up big margins in densely populated areas. So while voters have elected at least 244 Republican congressmen and probably will end up with at least 247 — more than in any election since 1928 — the map overstates their dominance.

But it does tell us something about the geographic and cultural isolation of the core groups of the Democratic Party: gentry liberals and blacks.

These were the two groups gathered together when Barack Obama had the opportunity to draw the new lines of his state Senate district after the 2000 census. He combined the heavily black South Side of Chicago with Gold Coast gentry liberals north of the Loop.

Together, they provided him with an overwhelmingly Democratic voter base and with access to the upper financial and intellectual reaches of the Democratic Party — and, in short time, the presidency of the United States.

But blacks and gentry liberals by themselves are not a national majority, as the map suggests. And policies designed to appeal to the Obama Democratic base may be repelling other, larger segments of the electorate. Consider the racial groups surveyed by contemporary political analysts.

1. Black turnout was only slightly down from 2012 to 2014 (from 13 percent to 12 percent of the electorate), and blacks voted 89 percent Democratic. But blacks are not a growing segment of the population, and Democrats will never again win by the margin Obama enjoyed among blacks in 2008 — 91 points, or 12 points of the entire electorate.

Democrats tried to gin up black turnout with ads about the fatal shooting of black teenager by a white police officer in Ferguson, Mo. But given the facts of the case that have come out so far, that may have hurt more than helped overall.

2. Hispanics represented 8 percent of voters in 2014 and 10 percent in 2012, and those percentages will rise. But they’re not unanimously Democratic. They voted 62 percent Democratic in House elections this year, but that figure was buoyed by the nearly 40 percent of Hispanics who voted in heavily Democratic California, New York and New Jersey. Hispanic Democratic percentages were significantly lower elsewhere, including Texas, Florida, Georgia, Kansas and Colorado.

Evidence suggests that gentry liberal causes — abortion absolutism, gun control, and opposition to fracking — have been repelling rather than attracting Hispanics. Polls also show they’re more interested in jobs and education — and dissatisfied with Democrats’ performance — than in immigration, on which they are miffed at both parties.

3. Asians, 3 percent of the electorate, have been oscillating wildly in exit polls: 73 percent to 26 percent for Obama in 2012, 50 percent to 49 percent for House Republicans in 2014. These may be small and unrepresentative samples. But note that California Asians squelched an attempt by gentry liberals, Hispanics and blacks to overturn the state’s voter-imposed ban on racial preferences in higher education.

4. Whites are constantly told they’re headed to minority status, but they were still 72 percent of voters in 2012 and 75 percent in 2014 — and they’re increasingly Republican. They voted 59 percent for Mitt Romney, the highest for any Republican presidential candidate except in the 1972 and 1984 landslides, and 60 percent for House Republicans this year.

Analysts who separate Americans into two tidy categories — white and nonwhite — assume that the nonwhite category will grow and that whites can’t vote any more Republican than they have historically. Presto, a Democratic America.

The first assumption is well founded. But Hispanics and Asians are not replicating blacks’ voting behavior, just as they haven’t shared their unique historic heritage. In some states they’re voting more like whites than blacks.

The second assumption may not be true at all. History shows that self-conscious minorities tend to vote cohesively, as blacks have for 150 years and Southern whites did for 90. It’s an understandable response to feeling outnumbered and faced with an unappealing agenda.

In that case, Romney’s 59 percent or House Republicans’ 60 percent among whites may turn out to be more a floor than a ceiling. And that map may become increasingly familiar.