David Siders writes for Politico about self-styled progressives‘ move to enforce a greater degree of ideological conformity.

Progressive Democrats are beginning to confront an unintended consequence of their own success: dilution of the brand.

So many Democratic presidential prospects are now claiming the progressive mantle in advance of the 2020 primaries that liberal leaders are trying to institute a measure of ideological quality control, designed to ensure the party ends up with a nominee who meets their exacting standards.

Leaders of the Congressional Progressive Caucus are discussing policy platforms that could serve as a litmus test for presidential contenders. Progressive donors, meanwhile, are plotting steps — ranging from closer engagement with campaigns to ultimatums tied to fundraising — to ensure that “Medicare for All,” debt-free college and a non-militaristic foreign policy, among other causes, remain at the center of the upcoming campaign. In an effort to winnow the burgeoning field, progressive advocacy groups are beginning to poll supporters in the hopes of elevating candidates who gain the imprimatur of the left.

“You don’t just get to say that you’re progressive,” Rep. Pramila Jayapal, co-chair of the Congressional Progressive Caucus, told progressive donors at a private conference here last week, a portion of which was opened exclusively to POLITICO.

Jayapal, a Washington Democrat, called the 2020 election a chance to “leverage our power.” But she called it critical “that we have some very clear guidelines about what it means to be progressive.”