Realignment

The two party system is a function of single member winner take all districts. Adopt proportional representation at the state level and we will look like PR. Many parties, 97% turnout. The LP and GPUSA may one day join coalitions (hard to imagine, they are used to being purists, which is why they are minor) and gain enough followers to be a major party, but only if we shift to proporational.
I used to be in charge of information for the DC Statehood Party, including member records and analysis. We had twice the voters as we did active registrants (most of our membership did not vote having moved or died and DC never purges so it can stop citizen initiatives). Actually, we had 2 Democrats for each party member in our voting base. Three times nothing is still nothing, even after we merged with the Greens.
Trump may drive out the non-racists from the GOP, turning it into a minor party. The Libertarian Republicans, maybe the LP and the Neo-Liberal DLC types could easily grab the White House in 2020 unless opposed by a coalition of Democratic Socialists Bernie Bots), Democratic Greens, Greens and some of those Libertarians in what would be a battle of ages (old v. young). Actually, it will be a battle for the ethnic vote. If the left can Occupy Capitalism and build a base in the workplace, it will have a better chance.