If the next Democratic president with a Democratic Congress wants any chance to pass a substantial legislative agenda after 2020, they need to be advocating for for the legislative filibuster to be eliminated. And their best shot is to start with legislation like the For the People Act, the voting rights and anti-corruption bill which the House passed on Friday, that unites the various factions of the party.

Republican Senate Majority Leader Mitch McConnell has already declared that the bill will not come to a vote in his chamber, which is logical enough: the electoral viability of the current Republican Party essentially requires that elections be unfair. More sobering, however, is the reality that, given unified Republican opposition, the filibuster — which requires 60 votes to end debate and thereby pass any legislation — would make it impossible for even a Democratic Congress and a Democratic president in 2021 to pass the bill.

But a Republican filibuster of voting rights and anti-corruption legislation would be the perfect vehicle to finally put an end to the anti-democratic practice.

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Most of the Democrats running for president, though, are denying (or pretending to deny) this reality. Of the current and former senators dominating the current Democratic field, only Sen. Elizabeth Warren, D-Mass., has suggested that the filibuster should be eliminated. (Some longshot candidates who aren’t attached to the Senate, including Washington Governor Jay Inslee, have been more receptive to eliminating it.)

This is not a disagreement that falls around ideological lines, either: Both former Delaware senator and vice president Joe Biden and Sen. Bernie Sanders, I-Vt., have disdained moves to eliminate the filibuster.

Relative moderates like Biden and Sen. Cory Booker, D-N.J., assert that the filibuster should be kept in place because it will force Democrats and Republicans to work together to develop bipartisan solutions, a fantasy discredited by pretty much everything to happen in American politics since Barack Obama’s inauguration. If the filibuster could restore bipartisan comity to American politics, it would have already happened.

Sanders’s theory is different but no more plausible. In explaining why he’s “not crazy” about getting rid of the filibuster, Sanders said in a recent interview that “the real issue is that you have in Washington a system which is dominated by wealthy campaign contributors.” Even if this true, it is beside the point: Not only would the dominance of big money in politics still exist after the next presidential election, the filibuster prevents bills that could change it from passing.

Claims that the next Democratic president and Congress can advance a substantial legislative agenda with the filibuster in place are clearly wrong. And the fact that the Democratic agenda is more popular than the Republican one doesn’t mean that public protest will compel Republicans to help a Democratic president get his legislative agenda passed. Instead, even if they are in the minority in the Senate, they’ll just use the filibuster, as they always have.

The legislative filibuster is a bad, anti-democratic procedure that should be eliminated. Just because most of the Democratic senators running for president — most or all of whom will still be in the Senate no matter who wins the Democratic nomination, after all — support keeping the filibuster not doesn’t mean that eliminating it is impossible. Senators tend to publicly voice their support for Senate norms until majorities feel the need to discard them. Mitch McConnell himself has made it his life’s work to dismantle long-standing norms he had long piously claimed to treasure.

But can Democrats ever be this ruthless? They can.

Consider the most relevant example: Senate Democrats decided in 2013 to end the filibuster for most judicial and all executive branch appointments. Many Senate Democrats — including liberals like Vermont’s Pat Leahy, then chairman of the Judiciary Committee — had been strongly committed to upholding Senate traditions and continued to observe them despite a conspicuous lack of reciprocation. But faced with the choice between upholding the filibuster as-is and allowing the Republican minority to prevent Barack Obama from getting any nominees to the nation’s second-most important courts confirmed, they decided to blow it up.

Another important lesson of the partial elimination of the filibuster is that Senate rules are just norms, and are most likely to be changed when the Senate majority has a compelling need to do so. The battle against the filibuster won’t be won based on abstract procedural arguments; the legislative filibuster will be substantially modified or eliminated when it stops a Senate majority from doing something that it really wants to do.

That’s not to say that it will be easy — and, especially if Democrats have only a 50- or 51-member majority in 2021, it will be very difficult. But the fact that many Senate Democrats are claiming to support the filibuster now doesn’t mean they’ll maintain their support in the future — and, in fact, they shouldn’t.