A few weeks ago, I wrote a piece headlined “The Bernie Sanders Surge Appears To Be Over.” The article (and, more emphatically, the headline) argued that Sanders’s rapid ascent in the presidential primary polls had slowed or stopped in polls of New Hampshire and Iowa, at least based on the polls we were seeing at that time. Ever since then, Bernie Sanders fans have been tweeting at me — sometimes kindly, sometimes not — after every new poll that showed their candidate doing well.

And guess what? They sorta have a point. Although his gains may not be as great as before, polls in August showed Sanders continuing to pick up support in New Hampshire (the situation in Iowa is less clear). But the fundamentals of the race haven’t changed very much. In particular, Sanders has shown little sign of winning over votes from African-Americans or Hispanics, which would limit his growth as the race moves on to more racially diverse states.

First, let’s talk a bit more about his recent gains in the polls, starting in New Hampshire. In the original article, I wrote that “Sanders rose from June to July in the Granite State, but his ascent slowed.” But Sanders picked up the pace in August, and support for Hillary Clinton has slowly dropped, according to live-interview polls. Here are the monthly averages:

IOWA NEW HAMPSHIRE MONTH CLINTON SANDERS CLINTON SANDERS August 47% 27% 37% 44% July 49 25 42 34 June 51 29 47 30 May 57 16 62 18

While the Sanders surge continued in New Hampshire, the polling in Iowa is more ambiguous. There was a lot of coverage of this weekend’s Des Moines Register poll (produced by top-notch pollster Ann Selzer), which found Clinton leading Sanders by just 7 percentage points, 37 percent to 30 percent. But Sanders’s numbers in Iowa, even in the Des Moines Register survey, have remained relatively consistent.

Clinton, on the other hand, continues to bleed support. The Des Moines Register poll was a bit of an outlier in terms of where it showed Clinton, but Selzer is so good at polling Iowa, you would be a fool to dismiss it.

So, Clinton’s margin over Sanders is at its lowest in both Iowa and New Hampshire. And while national polls weren’t the focus of my initial article, Sanders has also closed in on Clinton in those.

So why do I still think Sanders is a factional candidate? He hasn’t made any inroads with non-white voters — in particular black voters, a crucial wing of the Democratic coalition and whose support was a big part of President Obama’s toppling of Clinton in the 2008 primary. Not only are African-Americans the majority of Democratic voters in the South Carolina primary (a crucial early contest), they make up somewhere between 19 percent and 24 percent of Democrats nationwide. In the past two YouGov polls, Sanders has averaged just 5 percent with black voters. Ipsos’s weekly tracking poll has him at an average of only 7 percent over the past two weeks. Fox News (the only live-interview pollster to publish results among non-white voters in July and August) had Clinton leading Sanders 62-10 among non-white Democrats in mid-July and 65-14 in mid-August. Clinton’s edge with non-whites held even as Sanders cut her overall lead from 40 percentage points to 19.

There are other indications that Sanders is unlikely to win the nomination. He hasn’t won a single endorsement from a governor, senator or member of the U.S. House of Representatives (unlike Obama at this point in the 2008 campaign). Sanders is also well behind in the money race (again, unlike Obama). These indicators haven’t changed over the past month.

But even if you put aside those metrics, Sanders is running into the problem that other insurgent Democrats have in past election cycles. You can win Iowa relying mostly on white liberals. You can win New Hampshire. But as Gary Hart and Bill Bradley learned, you can’t win a Democratic nomination without substantial support from African-Americans.