I remain baffled by this argument that the left should pack this Supreme Court – with two new justices. Any court-packing strategy is going to carry a certain amount of risk, which means that if you are going to do it, you had better get something out of it. Two justices don’t justify that risk – and the case that this is somehow a safe or reasonable ask, in a way that four or six justices are not, is extraordinarily weak. Here are four arguments for six instead of two.

1. Two justices don’t even guarantee you a majority – but six do.

When Republicans refused to vote on the Garland nomination, they didn’t just steal a seat – they stole majority control of the court, which Democratic appointees would have gained for the first time since 1970. The liberal-left is not simply entitled to a seat or two. It is entitled to a controlling majority.

Imminent vacancies on the court threaten that entitlement, however. For the two-justice strategy to work, the liberal-left has to hope that the next president also gets to replace two of our three oldest justices. The arithmetic is quite simple:

In half of these scenarios, not even two new justices are enough to overcome a poorly timed vacancy – and the radical right majority remains in place. To ensure liberal-left control of the Court, activists have to call for at least six new justices.

2. Two justices do not remedy the Court’s dramatic rightward shift in recent decades – but six justices do.

This is because even if two justices gives the liberal-left bloc a majority, the most likely outcome would be a one-vote majority. As the above table indicates, this happens in two out of three scenarios where Democratic appointees win control, putting every decision at the mercy of the most conservative Democratic appointee. Remember when Justice Kagan voted to destroy Obamacare’s Medicaid expansion? She’s now the swing vote in every case.

Six justices don’t necessarily solve this problem either, since in the worst case scenario (Trump replacing Ginsburg and Breyer) court-packing would still only win the liberal-left bloc a one-seat majority. Nevertheless, in five out of six scenarios, six justices would expand the liberal-left bloc’s majority to at least three, giving it the breathing room it needs to advance a progressive agenda.

3. The risks of the two-and-six-justice court-packing schemes are probably comparable.

Simplistically, one could suppose that court packing schemes assume more political risk with every additional justice you nominate; this is the implicit logic behind calling for two justices, but not six. In practice, however, any court-packing scheme is going to face the same maelstrom of outrage from the right: attacks about broken norms, unconstitutionality, ascendant dictatorship, the politicization of the judiciary, the launch of a court-packing arms race, and so on. Whether we add one justices or a dozen, the same script will inevitably play out: Republicans will shift into full-throated DEFCOM 1 “our very Republic is in peril” mode; conflict averse, procedurally-obsessed centrists will wring their hands; and a handful of liberal flakes will grandstand and bravely defect.

Beyond that, what would matter is not the number of appointments so much as the stories one can tie to them. Ten appointments would give the right a “double digits” attack; nine would give them “doubling the size of the court”; and seven or eight would give them a “historically unprecedented” talking point. But six is the number effectively proposed by FDR; six has a story of political necessity behind it (see points one and two); and there just aren’t many attacks that you can make against six that you can’t make against less ambitious proposals.

4. Six justices is a strong opening bid for probable political negotiations.

So far I have given reasons why six new justices is the correct demand on the merits, the one that can guarantee the liberal-left control of the court and pull it out of the reactionary center – but there are also reasons why activists who are willing to settle for less (?) should be willing to increase their opening bid. Both have to do with the enormous pressure that even a two-justice proposal will face to scale back its demand.

First: if any of the adverse vacancy scenarios identified in point (1) materializes after the liberal-left has made two new justices our signature demand, we will be cornered: we will have to either abandon control of the court, or abandon our previous demand and ramp up to a new one. The shift in demands and rationalizations would play into the inevitable right-wing narrative that this is not a matter of justice, but a naked power-grab; it would be far less palatable than if we began with six justices as the reasonable baseline.

Second: even partisans of the two-justice strategy should recognize that political negotiations will pressure them to bargain down. The right will frame their ask as a hardball, uncompromising demand; centrists will call for some kind of deal (for example, the recurring proposal to impose term limits and regularize appointments); and the liberal-left, having settled on two justices, will have no room to maneuver. Make your demand six justices, and if this proves unpalatable, scale it back; this wins you the mantle of compromise and four to two appointments.

The six justice proposal provides a wide range of strategic and political advantages that the two justice proposal cannot. It has no additional liabilities. There is, as FDR said of his own six justice proposal, “nothing novel or radical about this idea.” If you want substantive and lasting justice on the Supreme Court in your lifetime, six new justices is where it begins.