In this polarized country, there is no such thing as 20% independent. The undecideds include a bunch of Sanders supporters who aren’t ready to say they will support Clinton, and a bunch of conservatives who can’t stomach Trump. By the fall, we’ll have the usual split of voters, with a tiny percentage who are too apathetic or clueless to make up their minds.*
It’s an interesting thought, but Trump will get a solid 35% from conservative voters who will never vote for Bernie or Hillary. Another 10% will vote Libertarian. That will leave 55% split between Clinton and Sanders. Worse yet, if young people don’t vote, Trump could win with super low voter turnout. And don’t forget about voter suppression laws which will affect Ohio, Florida, North Carolina and Pennsylvania.
*Remember 2004, when the public knew there were no WMDs in Iraq, Valerie Plame had been outed, and the clues were already accumulating that the CIA’s intelligence had been edited to sell the war? There were still people saying they wanted to hear more from the candidates after the last debate.)