Whoa! SurveyUSA has just come in with a national poll, conducted Sept. 2-3, showing Donald Trump leading Hillary Clinton 45 to 40 percent. Clearly even as Clinton's unfavorables are going up, Trump's are going down. The top line is not far out of line with national polls conducted between Aug. 11 and Aug. 30, which showed Trump with 41 to 45 percent and Clinton with 45 to 51 percent, but it is the first national poll showing Trump leading Clinton. But the biggest news in the SurveyUSA poll is its results for the "non-white" or "people of color" bloc that, in some psephologists' analyses, is fated to make the Democrats a permanent majority party.

Against Trump Clinton carries non-whites — but by less than impressive margins. Trump's name is supposed to be mud among Hispanics, but he gets 31 percent of their votes — more than Mitt Romney in 2012, the same as John McCain in 2008 — and Clinton gets only a bare 50 percent. Among Asians, Trump actually has a (statistically insignificant) lead of 41 to 39 percent, echoing the 50 to 49 percent Asian margin for Republicans in the 2014 vote for House of Representatives. And among blacks Clinton leads Trump by 59 to 25 percent. That's a huge contrast with Barack Obama's margins of 95 to 4 percent in 2008 and 93 to 6 percent in 2012.

Caveats:

(1) This is one poll. Polling theory tells us that one of every 20 polls is wrong, that is, its results vary by more than the statistical margin of error from what you would get if you could interview the entire population.

(2) It is a poll of 900 registered voters — a little smaller than the sample size for most other national polls. That means the margin of error is larger — and larger still for subgroups. SurveyUSA sampled about 108 blacks, 126 Hispanics and 63 Asians — or it sampled fewer and weighted their results higher.

(3) The SurveyUSA results for blacks and Hispanics are out of line with those in recent national polls by Public Polling Polling, Quinnipiac, and CNN/ORC. PPP has Clinton getting 83 percent from blacks, 65 percent from Hispanics and 53 percent from Asians — the first two numbers being fairly close to Obama's 2012 performance, the Asian numbers being significantly lower (see my next caveat). Quinnipiac has Clinton getting 91 percent from blacks and 67 percent from Hispanics — below Obama's 2012 percentages by statistically insignificant amounts. CNN/ORC has Clinton getting 72 percent from "non-whites" — ditto.

(4) All poll results for Asians should probably be disregarded. Do you believe the exit polls that said 71 percent of Asians voted for Obama in 2012 and 50 percent of Asians voted for Republican candidates for the House in 2014? I don't. I don't know which number was wrong and think perhaps both were. Asians — a category that includes people with roots in very different societies and very different immigration patterns historically — are about 3 percent of the electorate and spread very unevenly through the country. More than half live in just 14 major metropolitan areas.* My analysis of congressional districts with large Asian majorities (most of them safe Democratic) suggests a small shift, nothing like 20 points, toward Republicans between 2012 and 2014.

Those caveats having been registered, the black and Hispanic percentages in the Clinton-Trump pairings are worthy of notice, if they prove (and we'll see more in subsequent polls) to be anywhere nearly accurate. Trump is said to be hated by most Hispanics, yet he runs about as well as the last two recent Republican nominees among them, while Clinton runs about 20 points lower than Obama. The numbers for blacks are more astounding. They have voted more than 85 percent Democratic in every presidential from 1964 to 2012. Here they are voting only 59 percent for the woman who is married to the man who used to be called America's first black president and who served as four years as secretary of state for the man who is actually America's first black president.

Could this possibly be right? Maybe so, opine bloggers Mickey Kaus and Steve Sailer, who from very different points on the ideological spectrum favor significant cutbacks in immigration and who have had favorable things to say about Trump for that reason. Their hypothesis — and I think they don't advance it as more than that — is that blacks may see Hispanic immigrants as competitors for jobs and as driving down wages for unskilled work. Some analysts who lump "non-whites" together as a single bloc seem to believe that they see themselves as having a united interest in combatting white racism. But it seems implausible to me that most Hispanics and Asians — or that most blacks, for that matter — fear that whites want to impose pre-1960s Southern-style segregation on them or to disfavor them in more up-to-date ways. Certainly the "people of color" explanation is far less plausible than the Kaus-Sailer hypothesis.

Black Americans voted (where and when they were allowed to vote) overwhelmingly for Republicans in elections between 1868 and 1932 (backing Hoover over Roosevelt) and have voted overwhelmingly for Democrats in elections between 1964 and 2012. But in elections between 1936 and 1960 their votes were more evenly split, with the majority going to Democrats and a significant minority to Republicans (over 40 percent for Dwight Eisenhower in 1956, over 30 percent for Richard Nixon in 1960). It has seemed likely that blacks will never again vote as heavily Democratic for president as they did for Barack Obama, but most analysts (including me) have expected their Democratic percentages to fall only marginally. The SurveyUSA result and the Kaus-Sailer thesis both raise the possibility that blacks' voting behavior is about to switch to something more like the 1936-64 period.

That would be devastating for any Democratic nominee, as Washington Post analyst Philip Bump pointed out in a July 31 blogpost. Analysts arguing that Republicans need increased support from Hispanics have noted that if Mitt Romney had received in target states the percentage of Hispanic votes won by George W. Bush in 2004, he would have carried Florida, Colorado, Nevada and New Mexico, with a total of 49 electoral votes. But Barack Obama would still have won 283 electoral votes and the election. In contrast, if Obama had won only 65 percent of the black vote — a severe counterfactual, but one suggested by the SurveyUSA result — he would, by my back-of-the-envelope calculation, have lost Florida, Michigan, Ohio, Pennsylvania and Virginia, with 96 electoral votes — and Mitt Romney would be president. Turnout in 2012 in those states was 13, 16, 15, 13 and 20 percent black, and blacks there voted between 93 and 96 percent for Obama. A big shift in blacks' Democratic percentages — something everyone has hitherto believed inconceivable — could net Republicans a lot more electoral votes that any conceivable shift in Hispanics' Democratic percentages.

What are the chances of that actually happening? Pretty low, in my opinion. But not quite as low as I though a week ago. We psephologists have gotten pretty used to the patterns of partisan support that have largely prevailed from the late 1990s up through 2014. Some day they are going to change. Maybe that day is closer than we have assumed.

* Los Angeles/Riverside, New York, San Francisco/San Jose, Chicago, Washington, Honolulu, Seattle, Houston, Dallas, San Diego, Philadelphia, Boston, Sacramento and Atlanta. Note that the only 2012 presidential target states involved are (Northern) Virginia and (southeastern) Pennsylvania.