So I don’t necessarily disagree with your chart, but it’s neither statistically relevant nor comprehensive enough to draw any kind of firm conclusion. It’s really just a grossly oversimplified snapshot that includes people from all over the country, and it doesn’t correct for any other confounding variables. The source I linked in my first comment is much more comprehensive.

Progressive policies are broadly popular. Running on things that are popular tend to get you more votes. People like it when you do stuff for them.

Yes, I get that from an intuitive sense and based on scattershot polling. It’s a great sound byte, but it’s just a sound byte. You’ve not provided evidence of any of those propositions, and per my original response to you, the party is looking for electoral evidence, not intuitive suppositions.

The only evidence I’ve seen to the contrary is a NYT opinion piece that cites centrist think tanks and random people’s opinions. I didn’t see anything in there that looked reliable or compelling.

No offense, but the only “evidence” you’ve provided to support your assertion is a jpeg with 16 names on it, so I find your retort conveniently dismissive. They’re not “random people”, some of them are academics, and many of them are actual progressives. But fine, if you prefer that I be held to a higher evidentiary standard than you are, here’s what I can cobble together:

Combining a regression discontinuity design in close primary races with survey and administrative data on individual voter turnout, we find that extremist nominees—as measured by the mix of campaign contributions they receive—suffer electorally, largely because they decrease their party’s share of turnout in the general election, skewing the electorate towards their opponent’s party. The results help show how the behavioral and institutional literatures can be connected. For our sample of elections, turnout appears to be the dominant force in determining election outcomes, but it advantages ideologically moderate candidates because extremists appear to activate the opposing party’s base more than their own. (note: this was cited in my NYT source, so I assume you missed it)

Following previous literature, we use campaign donations to estimate the ideological positions of non-incumbent candidates. We f ind that in primary elections more extreme candidates receive more votes, and are more likely to win, than moderate candidates. However, the differences between extremists and moderates are small. More importantly, we show that the “reward” to extremism in the primary is swamped by an opposing reward to moderates in the general election. In general elections moderate candidates tend to receive more votes, and win more often, than extremists. (this one was, too)

I examine how the nomination of an extremist changes general-election outcomes and legislative behavior in the U.S. House, 1980–2010, using a regression discontinuity design in primary elections. When an extremist—as measured by primary-election campaign receipt patterns—wins a “coin-flip” election over a more moderate candidate, the party’s general-election vote share decreases on average by approximately 9–13 percentage points, and the probability that the party wins the seat decreases by 35–54 percentage points. This electoral penalty is so large that nominating the more extreme primary candidate causes the district’s subsequent roll-call representation to reverse, on average, becoming more liberal when an extreme Republican is nominated and more conservative when an extreme Democrat is nominated. Overall, the findings show how general-election voters act as a moderating filter in response to primary nominations. (this one as well)

My results support the notion that voters abstain due to indifference and imply that candidate positioning has a large effect on voter turnout and third party voting. Nonetheless, my results indicate that the candidates can best compete by adopting centrist positions. While a candidate can increase turnout among his supporters by moving away from the center, many moderate voters will defect to his opponent. (this one, too)

Using ideology measures derived from campaign contributions, we find that unsuccessful challengers in the U.S. House are generally more extreme than those who win, but ideological extremity is not a disadvantage to those seeking to represent an extreme constituency. More importantly, our existing political institutions may actually serve to mitigate the already high levels of partisan polarization in Congress.

And this source goes into a great amount of detail to address the “progressive paradox” that you’re highlighting, whereby progressive policies are ostensibly popular but progressive politicians less so. It suggests that how you frame progressive policies matters a lot to whether or not it’ll reach a receptive audience.

So yes, based on the evidence I can find the popularity of progressive policies does not translate into progressive victories. The Party is interested in electoral success, and if progressive politicians repeatedly fail to mobilize enough turnout to win elections except in the most ideologically pure districts, the Party is going to consistently hedge toward moderation on a national stage.