OK - there’s a thing called Duverger’s law. It’s quite simple.
If most elections are one-race/one-seat, single ballot, majority votes wins the seat, the system will tend to two major parties. Why? 3/

Imagine you have a country with one elected office only. There’s one ballot and one person will win. Let’s say you have many parties: greens 15%, libertarians 10%, liberals 30%, conservatives 35%, a few others 10%.
4/

If everyone votes for their own party’s candidate, conservatives win.
But, let’s say the greens and liberals would rather each other win than a conservative? They would form a pre-election coalition. Now we have the liberal-green party with 45% and conservatives with 35%. 5/

But - ho ho! Conservatives and libertarians can do that too! They join up to make the conservative-libertarian party and now its 45% vs 45%.

What happens next? They both fight over that remaining 10%.

6/

In this system, the coalitions are formed *before* the election, not after.

Now, let’s look at another form of election: at-large-member voting.

Let’s say we have a system with 10 elected people. All 10 represent the whole country on a council. 7/

The whole country votes and top 10 vote getters win (this can be done with everyone voting for one person, everyone voting for 10, multiple ways
8/

In this case, the greens want an actual *green* representative on the council, and with 15% of the vote, there’s a solid chance they can have one! Perhaps even 2 if they can sway some of those “others” who have no chance to vote green. 9/

So green votes green, let’s say they got 20% of “other” votes and win 2 seats. Liberals vote liberal and get 3. Libertarians get 1. Conservatives got some others and her 4.
There was no reason to form a preelection coalition. Coalitions will be negotiated decision-by-decision.10/

In the US, *all* of the congressional elections are one ballot/one seat elections. This is determined by the constitutions of each state. The presidential election, with the weirdness of the electoral college added in, is also one ballot/one seat. 11/

The US system pushes *pre* election coalition. And changing presidential elections alone won’t be enough to change it. Two parties will still organize around congressional elections and will be the dominant forces, thus dominating presidential elections too. 12/

There are many proposals to change this. All would require changing *state* election laws.
My fave was proposed by Lani Guinier: multi-member districts. Instead of carving up a city or rural region into multiple gerrymandered districts, make them one multi-member district.
13/

There are many other suggestions of changing voting systems without changing the one-district/one-seat set up.
You can read about some here. 14/
https://en.m.wikipedia.org/wiki/Cardinal_voting

So - to Ryan Knight’s tweet:
1. If he really wanted a left party, he would not be working to drag Democrats but to change state voting laws. As it is, he is just harming the center/left coalition.
2. Also his tweet is complete nonsense in terms of the positioning.
/end.