It's less likely for two stable parties to make up 90% of the electorate in such a system, because splitting parties is much easier. If the US had proportional

It's less likely for two stable parties to make up 90% of the electorate in such a system, because splitting parties is much easier. If the US had proportional representation, there's no way Nikki Haley and Marjorie Taylor Greene would be in the same party, nor Bernie Sanders and Kamala Harris. But this split will never happen in the current system because leaving one of the two major parties would be electoral suicide. There are ten factions represented in the Knesset (Israeli parliament) and the biggest one (Likud, Netanyahu's party) got 23% of the vote in the last election. It's true that fringe parties can have outsized influence in a proportional system, but the US system suffers from the opposite problem: fringe elements can take over one of the major parties, which seems to be well on its way to happening with the Republicans now.