With one of the last big developments in the Democratic race in the rear-view mirror (farewell, Joe Biden!) and on the eve of the second Democratic debate on Saturday, a just-released New York Times/CBS News poll shows a familiar picture. Hillary Clinton has a large, consistent lead over Bernie Sanders, and while Martin O'Malley is seeing some O'mentum, he's still only at 5 percent. (I am deeply sorry for that, by the way.)

The big picture -- the Real Clear Politics polling average -- shows that not much has changed recently. The Biden decision not to run boosted both Clinton and Sanders, to some extent, but Clinton's still got a large lead.

A week earlier, a Fox News poll had similar numbers. NYT/CBS was Clinton 52, Sanders 33; Fox was Clinton 56, Sanders 31. Fox also broke out the split among white and non-white voters, which we keep coming back to. Mostly because it looks like this:

Clinton leads among whites by 13. She leads among non-white voters by 45.

Sanders recognizes that this is a problem. The campaign's plan is to win Iowa and New Hampshire and then peel enough of the non-white (specifically, black) vote in subsequent states so that they can have a shot.

Those things are related, the winning Iowa and New Hampshire and then doing well enough with black voters. If we compare the upcoming primary schedule with 2008 exit poll data on the composition of the Democratic electorate (where available), you can see that Iowa and New Hampshire's white electorate quickly becomes the exception, not the norm.

Sanders, as the Fox News poll shows, is also losing nationally among white voters. But in past polls he has run even with or passed Clinton among whites (often with Biden splitting Clinton's base). Which raises an interesting question: Could a Democratic primary candidate win the party's nomination without strong support from non-white voters?

Most voters in both parties are white. Nearly all Republicans -- from moderates to the most conservative -- are white, according to data from the General Social Survey, and that's been the case for decades.

But notice that the percentage of "strong Democrats" that is white has slipped since the 1980s. Back then, two-thirds of strong Democrats were white. In 2014, about half were. Most of the difference has been made up by blacks -- 30 percent of the group in 1984 and 39 percent last year.

We noted in July that the black vote has become increasingly important to Democrats in federal elections, as below.

Bernie Sanders's halted momentum might make this unimportant for 2016. But it's easy to see a future campaign in which a rift between black and white Democrats creates tension on the march toward the nomination.

Or, actually, it's easy to see a past campaign that does that. In 2008, black Democrats backed Barack Obama 82-15 over Clinton. Whites backed Clinton 55-39 -- a split that Sanders only wishes he had to deal with.