The latest NBC News/Wall Street Journal poll shows Hillary Clinton with a narrow three-point lead over Donald Trump, 46 percent to 43 percent. But if Bernie Sanders were out of the race the NBC News political unit estimates her lead would likely be much larger, perhaps up around eight points, 51 percent to 43 percent.
The difference in those two scenarios is one kind of voter that pops in many polls: The Sanders-only supporter.
The latest set of presidential polls shows two very different races - the tight three-point battle between Clinton and Trump, and a much larger lead for Sanders over Trump. The NBC News/Wall Street Journal poll had Sanders with a whopping 15 point lead over the presumptive GOP nominee, 54 percent to 39 percent.
Of course, the real meaning of those differences is hard to determine. At this point the odds of Sanders-Trump election in November are steep. Clinton is on the verge of capturing the Democratic nomination - she needs fewer 80 delegates to reach the 2,383 required to win.
Could Clinton win those Sanders-only supporters if she becomes the nominee? Maybe not all of them, but a good deal of the current hard feelings have come from the protracted fight for the Democratic nod.
In terms of policy and politics, most Sanders supporters are probably more in line with Clinton than Trump. They voted in Democratic nominating contests and polls show most of them are more politically liberal than Clinton supporters.
So to get a better look at where the Clinton-Trump race might stand after the nominating dust has settled, we recalculated the latest NBC/WSJ poll with Clinton capturing 70 percent of the Sanders-only vote.
The result: those Sanders-only voters are worth an extra five points to Clinton. In the NBC/WSJ poll, Clinton's advantage over Trump goes from three points to eight points and she leads 51 percent to 43 percent. But the difference holds in other polls as well.
In the latest CBS News/New York Times poll, Clinton's advantage grows from six points to nine points with 70 percent of Sanders-only voters - she leads 50 percent to 41 percent. In the latest Fox News poll, where Trump currently leads Clinton, the Sanders-only voters make it a tied race - 45 percent to 45 percent.
Much of this is theoretical. No one knows for certain how many Sanders-only voters will support Clinton. And with time it's possible Trump's support could grow as well as undecided voters make choices. He could also win some of the Sanders vote.
But the larger point is, the current batch of polls is coming at an odd point in the race, one where Republicans voters have begun coalescing around Trump, while Democrats still remain divided.
History suggests that will change. And more important, these numbers suggest two very important points about the Democratic race for president right now.
The three-to-five points in the polls above are critical to Hillary Clinton if she wants any comfort in a race against Donald Trump. And that means, whether he wins or loses in the remaining nominating contests, Sanders is in a very strong position to get concessions from Clinton and the Democratic Party.
For Clinton, the Sanders-only voter may hold the keys to the White House.
This story first appeared on NBCNews.com.