How does that increase scope for third parties? If only two can be on the ballot in the general election, doesn’t that just reinforce the idea that it’s a two-party system?
Has the use of this system in California resulted in more parties getting electoral support?
Yes and that was a disaster with Q promising Clay the Secretaryship of State in order to get his votes. Incidentally, the choice in the House is by states, not representatives, with each state having one vote. Since, for example, PA is 9-9, they would be unable to vote. It is the worst electoral system imaginable. Nearly.
Jefferson/Burr was the only other example and that was pretty disastrous too.