For Democrats, the main issue in the shutdown wasn’t electoral backlash — it was the filibuster. Leadership feared its removal, viewing it as a safeguard to keep the party’s rising left wing in check.

The Democratic leadership doesn’t want to get rid of the filibuster for the same reason the Republican leadership doesn’t want to get rid of it: The filibuster allows the leadership of both parties to keep their radical flanks at bay. Chuck Schumer needs the filibuster to protect himself from the Bernie Sanders wing in the Senate and the Alexandria Ocasio-Cortez (AOC) wing in the House: if you can’t get to sixty, Bernie and AOC, we have to follow the lead of Joe Manchin and Kyrsten Sinema. Same goes for John Thune to whoever inhabits the radical role at any given moment in the GOP.

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For Trump, swap in Trump’s most rabid allies and foot soldiers in the Senate and the House — or Schumer’s and Hakeem Jeffries’s enemies in the Senate and the House — and you get a pretty clear sense of why the leaderships of both parties need the filibuster: It checks anyone who “defies party orthodoxy,” while providing “an excuse to avoid doing things.”