The central challenge for Democrats in taking back the White House will hinge on the party’s ability to persuade a majority of Americans to support a more progressive agenda going forward.
Apparently, Mr. Sosnik isn't familiar with how the Electoral College works. A plurality of Americans already vote democratic, and have so in all but one presidential election since 1992. Democrats' problem isn't one of majorities; it's one of geographics. That is unlikely to change anytime soon, and moving further leftward will accelerate, not decelerate this phenomenon.
The leftward lurch has some real perils in it. The numbers cited above I think don't paint the whole picture. Immigration, e.g., wasn't much of a partisan fight until like 2015 when the Muslim Ban was first proposed. Immigration reform was the darling of W and the Kochs and was opposed by Bernie Sanders as recently as the beginning of the primary season. That dramatic 52 point shift has seen a lot of its movement only in the last couple years. Similarly, we're seeing a dramatic increase in "single payer" devotees in just the last half year. Democrats and liberals should be wary of getting caught in the "against Trump" vortex, and not let it color their chances of ever winning another presidential election.
Speaking of, NYT published an OpEd today calling for Al Franken's resignation. That's the level of crazy liberals are going to rise to in service of all things "against Trump". Of all the moronic OpEds NYT has published over the years, this one got me particularly pissed off (because when Erik Prince or John Bolton publish one they're easy to laugh off), because it represents the worst of the left mob: letting a staff writer (as opposed to a one off partisan) call for the head of one of America's finest senators because, well, Roy Moore is a child molester and Donald Trump is a rapist and we don't like them so everyone gets a trophy.
People need to keep their heads. America and the Democrats don't need a leftward push, especially one that's driven by "against Trump". We need a push toward sensible regulatory and tax reform, driven by a shared sense of community and compassion. That's not a leftist agenda, even though it sounds like one in today's world. It's a humanist agenda that the left has the best mandate to push. It will only happen, however, if we move past the identity driven leftism that's currently en vogue.