Joe Biden is out a new ad that emphasizes his ties to former President Barack Obama — and to mark the 11th anniversary of Obama choosing Biden as his running mate.

Alan Abramowitz: “When it comes to ideological identification, Democratic voters are far more divided than Republican voters. Around two-thirds of Republican voters identify as conservative while fewer than half of Democratic voters identify as liberal. Many observers of the current presidential campaign have cited this fact to argue that ideological divisions are a serious potential threat to Democratic unity, especially if the party nominates a strongly liberal candidate.”

“But a closer examination of recent polling data indicates that when it comes to specific policy issues such as abortion, gun control, and health care, Democratic voters are actually considerably less divided than Republican voters. Moreover, these data show that divisions among Democrats based on age, education, and race are much less significant when it comes to policy issues.”

“What makes this all the more important is that policy preferences appear to have a much stronger influence than ideological identification on voters’ broader political outlook including their opinions of President Trump. These findings suggest that the task of uniting Democrats behind the party’s eventual nominee may not be as difficult as some pundits and political observers have suggested.”

Jonathan Bernstein: “It’s been a very long time since a true dark horse — a candidate who really came out of nowhere — won a presidential nomination. But we’ve had a couple of recent winners (John McCain in 2008 and John Kerry in 2004) who looked dead in the water for long periods of the year before the election. And we’ve had other candidates (Rick Santorum in 2012 and Gary Hart way back in 1984) who showed almost no signs of life until right before the Iowa caucuses but then went on to become serious challengers to the eventual winner.”

“I see a lot of pundits out there who want to reach conclusions about at least the structure of this cycle’s nomination struggle, if not proclaim a winner. I’m not averse to doing that when there’s strong evidence, as there was for Hillary Clinton in 2015. But there’s nothing close to that this time, and that means, to me, that we still don’t really have a good idea of where any of this is headed.”

New York Times: “Some Trump advisers are more concerned about a primary challenge than they publicly let on, as Mr. Trump faces more strain in the job than he has in many months. They are also aware that primary challenges can weaken incumbents in a general election. The most recent example was President George Bush, who faced a primary challenger from the right in 1992 from Patrick J. Buchanan, a former aide to Richard Nixon and a prominent conservative…”

“Some public polling has found that more than 40 percent of Republicans are open to a primary challenge to Mr. Trump.”