Negotiations over the Deferred Action for Childhood Arrivals program are complicated, but at their most basic level involve Democrats asking Republicans to codify protections for Dreamers and Republicans asking Democrats to allocate more resources to border security in exchange for those protections.

In a midterm election year where Democrats, especially in the Senate, are defending key seats in states the Republican president won last cycle, you would think funding border security — or supporting provisions on chain migration and the diversity lottery — would be a common-sense decision.

But not for today's Democratic Party.

A loud and influential coalition of grassroots progressives has applied enormous pressure on the party for months to demand a clean Dream Act from Republicans and nothing less. That, of course, is a nonstarter for the GOP. As far back as September, House Minority Leader Nancy Pelosi, D-Calif., was shouted down by activists outraged over her decision to negotiate a DACA deal with President Trump in exchange for border protection measures.

Radical progressives now constitute a significant portion of the Democratic Party's base. Consequently, Democrats are now facing intense pressure to do what's best for someone like Sen. Dianne Feinstein, D-Calif., at the expense of someone like Sen. Claire McCaskill, D-Mo. Tellingly, seven out of the 10 senators running for re-election in states the president won voted last month to resist the Resistance, choosing to support a stopgap bill that funded the government without including DACA protections. Under pressure from her primary opponent, Feinstein changed her mind and voted against it.

Can the party of Feinstein survive in Missouri?