Warren has two obvious problems with party elites. First, there is the perception among some of them that her left-wing stands, such as Medicare for All, are too risky for the general election and decrease the party’s chances of defeating President Trump. For example, House Speaker Nancy Pelosi has not outright endorsed Biden or specifically declared that she does not support Warren, but Pelosi has argued that the party needs to have a big, sweeping electoral victory in 2020, and that such a win requires more moderate policies, like focusing on improving Obamacare instead of pursuing Medicare for All. Those are sentiments decidedly on the side of Biden and Mayor of South Bend, Indiana, Pete Buttigieg and against Warren and Sanders.

Secondly, electoral considerations aside, there is a center-left wing of the Democratic Party that fundamentally disagrees with Warren’s more leftward positions. It’s hard to imagine some of these figures endorsing Warren before she has effectively already won the nomination. (That fits with Shor’s findings — Warren’s endorsers at the state legislative level are more liberal than the endorsers of any of the other candidates.)

These problems are not unique to Warren. Sanders was perceived as too far to the left by many Democratic elites in 2016; he got very few endorsements back then and is not getting many this cycle, either. (Sen. Amy Klobuchar actually leads Sanders in endorsement points.)

Warren also has a third challenge with party elites that is less obvious. The Massachusetts senator clashed with senior aides to President Obama for much of his tenure in the White House. She, like Sanders, isn’t quite in line with the party’s establishment. A Warren administration would probably be less likely to hire former Clinton (Bill and Hillary) and Obama aides in key posts than, say, a Biden, Booker or Harris one. So people connected with the party establishment (like many DNC members) may be fine with Warren but prefer other candidates for more self-interested reasons.

The endorsements we’re focused on miss some of Warren’s support

For a variety of reasons, we opted not to track endorsements from groups (as opposed to individuals). So that leaves out, for example, Warren winning the backing of the Working Families Party, a liberal activist group that has chapters in 15 states and is influential in places like New York. Several of the other candidates, including Sanders, pushed hard for that endorsement, and it may be more valuable than the backing of a handful of members of Congress.
A strict count of formal endorsements also leaves out less official institutional support. The liberal activist groups under the broader “Indivisible” umbrella, MSNBC (particularly its more left-leaning hosts like Rachel Maddow) and Pod Save America aren’t likely to endorse a candidate in the Democratic primary. But the general ethos of those organizations is closer to “Republicans are morally bankrupt and must be confronted aggressively,” than “Democrats can work with Mitch McConnell.” (Biden hints at the latter, Warren the former.)

Lara Putnam, a historian at the University of Pittsburgh who has studied Democratic activist groups like Indivisible that have emerged after the 2016 campaign, says that many individual Indivisible chapters don’t want to formally endorse a candidate in the primary. They fear endorsements would create divides and make it harder for those groups to unify for the general election. But Putnam also says that many of the activists involved in post-2016 anti-Trump organizing are backing Warren. And they are acting on that support through, say, Facebook groups that are separate from the respective larger anti-Trump groups these activists are also affiliated with. (An informal August poll done of its members by national Indivisible also showed Warren as the activists’ favorite.)

“Warren has a large number of potentially very influential supporters in the local grassroots space, and they are also the people most opposed to using public endorsements as a means of pressure to shape [the] primary contest,” said Putnam.

Similarly, we are tracking the designated Democratic leader in state legislatures around the country, so we counted Georgia House Minority Leader Robert Trammell’s endorsement of Harris, for example. But the endorsement of Warren by Lorena Gonzalez, a rising star in the state House in California, a hugely important primary state, isn’t captured in the FiveThirtyEight tracker, even though Gonzalez’s backing may be more significant than Trammell’s. Molly Kelly, who was the Democratic nominee for governor in 2018 in New Hampshire, is also backing Warren; that’s another fairly high-profile endorsement that doesn’t fit our metrics. Warren has the most endorsements from state legislators in Iowa, which might be more significant than federal legislators or state legislative leaders.