In 2000 there was polling showing McCain at 24% vs Gore at 34% and Bush at 35% had McCain run Reform. Historically he didn't so, probably wisely.
Let's say McCain is feeling particularly angry after South Carolina and takes the leap. He gets Angus King of Maine to be his running mate.
Lieberman opts not to be Gore's running mate, not wanting to run against his friend John. Gore is more concerned with centrist voters than historically and thus picks an even more centrist running mate - Evan Bayh.
Gore's increased focus on the center boosts Ralph Nader who polls better than historically. Furthermore, Nader gets Congresswoman Cynthia McKinney (who was speculated as a running mate historically) to be his running mate. Nader historically peaked at 6% polling in June 2000 (4.5% average in July, 3% average in August) but here he gets up to 10%.
Come debate time, Bush is polling 37%, Gore is polling 34%, McCain is polling 19%, and Nader is polling 8%.
McCain satisfies the criteria and is invited to the debates. Bush, seeing McCain as mostly hurting himself, calls for Nader's inclusion. McCain likewise calls for Nader's inclusion. Gore ultimately acquiesces and says he supports Nader's inclusion.
Thus, the debates end up being 4-Way. As for how the election goes, I'm thinking of writing a timeline on this concept and don't wanna give it away.
Thoughts?