Justin Amash Could Cause Some Trouble In November

The 2020 presidential election just got its first notable third-party challenger. Last Tuesday, Michigan Rep. Justin Amash, who left the Republican Party nine months ago and became an independent, announced he would run for president as a Libertarian. And while we won’t know whether Amash wins his new party’s nomination until later this month, here’s what we do know about third-party candidacies more broadly and what that could mean for President Trump and former Vice President Joe Biden in the general election.

First, it’s unlikely Amash wins much of the...