Gilens, Page and their critics basically agree on the same set of facts. Their differences emerge from their conflicting interpretations of those facts.

Take the enactment of Obamacare. For Gilens, the final legislation reflects the failure of the Democratic Party to achieve progressive goals:

In 2009, with unified Democratic Party control and a filibuster-proof majority in the Senate, the Democratic Party failed even to include a public option in Obamacare, much less establish a health insurance program that would cover all uninsured Americans.

The Affordable Care Act, Gilens continued, is “one illustration of the power of interest groups in constraining Democratic Party policy.”

Critics of Gilens’ argument contend that enactment of Obamacare marks the first major downwardly redistributive federal legislation in generations, a major progressive achievement after decades of conservative success in distributing income and wealth to those in the top brackets.

“The A.C.A. was less sweeping than it could have been because of the constraints imposed by a powerful health care lobby, but it was more sweeping than anything that had come before,” Rhodes wrote by email. “The fact that significant health care legislation was enacted in spite of substantial resistance was a testament to the strength of progressive mobilization at the time.”

In other words, for Gilens, the glass is half empty, for Rhodes, half full.

Grossmann and Isaac write:

The view associated with Bernie Sanders and some scholars, which suggests that both parties have been bought off by rich donors to represent the rich and big business at the expense of the middle class, is inconsistent with the patterns we observe.

The Republican Party, they contend, perhaps unnecessarily,

does seem consistently responsive to business preferences and its positions are more often associated with those of the affluent. On economic policy in particular, Republican leaders much better represent affluent and business preferences.

But the Democratic Party, Grossmann and Isaac argue, “is not aligned with business preferences or affluent preferences in any domain — and actually represents middle-class views over affluent views on economic policy.”

Along similar lines, Rhodes and Schaffner found in their 2017 paper that:

Individuals with Democratic congressional representatives experience a fundamentally different type of representation than do individuals with Republican representatives. Individuals with Democratic representatives encounter a mode of representation best described as “populist.”

In contrast, they continue,

individuals with Republican representatives experience an “oligarchic" mode of representation, in which wealthy individuals receive much more representation than those lower on the economic ladder.

In an email, Rhodes noted that

Democrats are on average more responsive to their less affluent constituents than they are to their more affluent constituents, while for Republicans the reverse is true.

If the standard in judging the Democratic Party is whether it would support a radical upheaval vastly expanding the federal government, Rhodes continued, then

it’s fair to say that few elected Democrats at the national level are contemplating major departures from prevailing economic and political arrangements. There’s little evidence that most elected Democrats want an economic “revolution.”

But, Rhodes continued, “the reality is more complicated” than the Sanders claim that “the party is dominated by corporate interests and is unresponsive to the demands of the working and middle classes.”

Instead, according to Rhodes,

there’s a decent case to be made that many Democratic elected officials are indeed representing their working- and middle-class constituents by taking moderately liberal positions on most economic issues.

Interestingly, the progressive wing of the Democratic Party faces another challenge from an unexpected source.