You’re pissing in the wind since the United States has been more or less a two-party system since the 1790s. It’s not in the Constitution but those pesky founding fathers (save for George Washington who hated the idea of any parties, even just one of them, let alone two or more) seemed to warm up to the idea pretty quickly.
Your best bet is for a party that closely aligns with what you believe splinter off and that splinter group becomes the second party while the ones who stayed behind get lost and wither away.
And let’s face it, the American history of third parties is pretty shabby.
Ralph Nader was an egomaniacal blowhard whose useful days were way behind him when he decided to play spoiler. H. Ross Perot was insane, racist, cantankerous and unfit for office. The Libertarians are… Libertarians, a joke if there ever was one.
The Know Nothing Party made a little noise and helped hasten the demise of the Whigs in the 1850’s but honestly, they were a footnote notable only because they seem to have been revived with the Trump movement:
[QUOTE]
By 1856, the Know-Nothing party was in decline. Many Know-Nothing officeholders were relatively unknown men with little political experience. In the states where they gained control, the Know Nothings proved unable to enact their legislative program, which called for:[ul][li]a 21-year residency period before immigrants could become citizens and vote;[/li][li]a limitation on political office holding to native-born Americans, and[/li][li]restrictions on liquor sales.[/ul][/li][/QUOTE]
They weren’t keen on Catholics either.
Your best bet is to have a Parliamentary System where multiple parties are more common. I would have said this wasn’t likely, but given the complete stop that Republicans have done because they didn’t like Obama (and surely will not change much under Clinton), maybe having a leader who is voted in with a majority of a parliament is what we need to actually, you know, pay our bills and other icky stuff governments are supposed to do.
I’m still not really sure that we can make such a drastic change even as one party decides that actual governance is bad, but that’s your best bet if you really want to tear the system down and two parties aren’t enough to satisfy you.
ETA: And another perfect example why a third party isn’t a panacea for our problems — Maine. Ask any Mainer what they think of their governor who won his first term with barely a third of the vote thanks to two independent candidates on the ballot and then got reelected with less than half the vote thanks to another independent on the ballot. So how did that third party influence help Maine exactly?