Michael Barone devotes his latest column to the oft-repeated assertion that America’s changing demographics doom the Republican Party to eventual obsolescence.

Republicans are often told that their party is headed toward minority status because of the rising numbers of heavily Democratic non-whites. Many analysts, even the perspicacious Ron Brownstein of National Journal, tend to lump all non-whites together.

But the three categories of non-whites — blacks, Hispanics and Asians — are strikingly different in partisan terms.

Blacks, 13 percent of the electorate in 2008 and 11 percent in 2010, are almost unanimously Democratic and remain so this year. They’ve been about 90 percent Democratic since 1964.

But they are not a rising percentage of the population. And in post-Obama America, they may find themselves split on issues, with some switching parties, as members of other ethnically defined groups have done historically. Even this year, they tend to oppose same-sex marriage, the opposite of the position Obama took last May.

Hispanics were 9 percent of the electorate in 2008 and 8 percent in 2010. Those percentages will rise as young Hispanics come of voting age — but probably not to the levels suggested by straight-line extrapolations from the years of heavy Hispanic immigration from 1982 to 2007.

Since then, more people have migrated to Mexico from the United States rather than the other way around. The most recent immigration figures show more Asian than Latin immigrants.

Recent polls suggest that Obama may run even stronger among Hispanics than his 67 to 31 percent margin in 2008. That will help him in target states Colorado and Nevada. But polls in the biggest target state, Florida, show Hispanics about evenly divided, even though less than half are Cuban-Americans.

Republicans got 38 percent of Hispanic votes in 2010, enough to win the total national vote. In the future, Hispanics are likely to vote more Democratic than average, but not hugely so. And they’re likely to become 12 to 15 percent of the electorate someday, not 20 or 25 percent.

The third group of non-whites are Asians, 2 percent of the electorate in 2008 and 2010. They’re the least Democratic non-white group, 62 percent for Obama in 2008 and 58 percent for House Democrats in 2010. Current polling suggests similar numbers this year.

But Asians aren’t a single cohesive group and may not be reliably Democratic over time. They voted Republican for president in the 1990s.