Biden is ahead because he is consolidating his support among non-white voters, a key voting bloc among whom he already had a very clear edge over his primary rivals.
Here's how the numbers by race break out in the new CNN poll:
Whites

Biden 27%
Warren 23%
Sanders 15%

Non-Whites

Biden 42%
Sanders 16%
Warren 13%

That's striking stuff. And while Biden has long led among non-white voters, his support has surged since earlier this fall when he was taking just 28% of their vote in a hypothetical Democratic primary ballot.
Why is his support among non-white voters -- and the suggestion that support is increasing as actual votes near -- so important for Biden and his chances? Because non-whites have been the decisive voting bloc in each of the recent contested Democratic presidential primaries. In 2008, Barack Obama beat Hillary Clinton because of his massive edge over her among black voters. Eight years later, Clinton beat Sanders because she crushed him among African Americans and Hispanics.

Bonnen’s political future was first called into question in late July, when hardline conservative activist Michael Quinn Sullivan, who heads the group Empower Texans, revealed that Sullivan, Bonnen and one of the speaker’s top allies had met at the Texas Capitol the month before. At that meeting, Sullivan alleged, Bonnen and state Rep. Dustin Burrows, R-Lubbock, suggested Empower Texans go after a list of 10 House Republicans and told Sullivan his group could have media access to the lower chamber in 2021. Bonnen also disparaged multiple Democrats, calling one “vile” and another “a piece of shit.”

A majority of members were at first unsure of what to think about the allegations, given that Sullivan was a longtime critic of House leadership and that their new speaker had overseen a legislative session that was hailed largely as a success. The allegation that Bonnen had planned to politically target members from his own party also seemed to contrast what he had announced on the last day of the session: If an incumbent targeted another colleague, regardless of party, there would be consequences.

Facebook on Monday said it removed a network of Russian-backed accounts that posed as locals weighing in on political issues in swing states, praising President Trump and attacking former Vice President Joe Biden, illustrating that the familiar threat of Russian interference looms over the next U.S. presidential race.

Facebook said the network bears the hallmark of the same Kremlin-backed group that interfered in the 2016 election by sowing social discord, boosting Trump and attacking Democratic candidate Hillary Clinton. The new disinformation campaign appears to follow the same playbook.

This time, a coordinated group of Russian accounts that appears to show some links to the Internet Research Agency took largely to Facebook’s photo-sharing app, Instagram, to post content this year about U.S. politics and memes targeting Democratic presidential contenders.

The operation demonstrated a sophisticated understanding of the schisms within the Democratic Party as it labors to choose a nominee to face Trump next November. One Russian account, which portrayed itself as as a black voter in Michigan, used the #blacklivesmatter hashtag to hammer Biden for his gaffes about racial issues. Some of the accounts boosted one of his left-wing rivals, Sen. Bernie Sanders (I-Vt.).

To begin with, 33 percent of voters say their vote in 2020 depends on whom the Democrats nominate. Of these, 61 percent are moderate and 54 percent identify as independent, while the rest are more inclined to identify as Democrats (21 percent vs. 15 percent) than Republicans. They are also younger, more likely to be Hispanic and more likely to have an education of high school or less. Thirty percent voted for Hillary Clinton, 18 percent voted for President Trump. We also know candidates’ position on issues is the most important factor (43 percent) as opposed to leadership experience or style.

Depending on which states, these “it depends on who the Democrats pick” voters could be critical. Moderate candidates (e.g., former vice president Joe Biden, Sen. Amy Klobuchar) might appeal to these voters, but a younger candidate (South Bend, Ind., Mayor Pete Buttigieg) might excite them. One thing we know: These are not the college-educated white, super-progressive Democrats attracted to Sens. Bernie Sanders (I-Vt.) and Elizabeth Warren (D-Mass.).

In addition, there is a whole lot of soft Republican support. Fifty percent say they approve of Trump’s performance but that Trump could lose their support. This is quite different than the portrait of an immovable GOP base that one hears about. By contrast, only 15 percent of Democrats say they disapprove of Trump but that he could win them over. Weak Trump supporters include many college-educated voters (Trump draws only 36 percent of these) and female voters. In short, the right Democratic candidate could peel off some, albeit not a lot, of Republican support.

Finally, 54 percent put terrorism in their top three issues, including 51 percent of independents. While Democrats have chosen to focus on the international repercussions of the pullout of troops from Syria, freeing thousands of Islamic State fighters should be of major concern to a majority of voters.

The leading presidential contenders continue to debate Medicare for All, a sweeping new government program that would replace private insurance and require trillions of dollars in new federal spending. Senators Elizabeth Warren and Bernie Sanders are the biggest backers. Former Vice President Joe Biden favors more modest changes that would keep private insurance in place but offer more government help for people who can’t afford a private plan.

Voters seem to be siding with Biden. New polling by the Kaiser Family Foundation shows 51% of people favor Medicare for All, down from 59% last year. Other polling shows support for Medicare for All plummets when people realize it would mean abolishing private insurance and raising taxes.

The Kaiser survey, meanwhile, shows 73% of people favor a more limited public option that would keep private insurance in place. That’s up from 65% earlier this year. Among Democrats, 71% support Medicare for All while 85% support a more limited public program.