As many pundits have pointed out in recent months, the Democratic primary electorate is far from uniformly liberal. In fact, the median Democratic primary voter is largely insensitive to intraparty ideological divides (the most popular second choice among Joe Biden voters is Bernie Sanders, and vice versa).

But the median Democratic voter – who closely monitors primary campaigns eight months before the first Iowans cast their ballots – is a different animal. Democrats who pay a lot of attention to politics tend to be more ideological, and ideologically left wing, than those who do not. And these high-information, highly progressive voters include potential campaign volunteers, activists, policy staff, partisan pundits, and small-dollar donors— people whose power to influence the primary’s outcome extends well beyond their behavior in the ballot box. This predominantly progressive voting bloc can shape media narratives, staff get-out-the-vote operations, vouch for a candidate with broader constituencies, and help keep a campaign funded. Before the advent of small-dollar digital fundraising, the influence of money in politics was the bane of the left’s existence; in the 2020 primary, it’s arguably a source of left-wing strength.

For these reasons, Democratic candidates have some incentive to favor the strongly held preferences of their party’s highly engaged, progressive minority over the (often weakly held) moderate preferences of its broader base on issues where there is a divergence between the two.

And yet, if progressives are overrepresented in the political discourse and presidential primary debates, they are systematically underrepresented in Congress.