Independents may well be willing to listen to election reforms moving forward, but they are not interested in the past. And Trump's obsession with that is leading many of them to conclude that he's not fit for office.
Prior to being elected in 1980, Reagan had run on privatizing Social Security, and eliminating or returning to the states Medicare and Medicaid. He learned after he was elected that there was not sufficient support to do that, so rather than beating his head against an unpopular topic and hurting his popularity, he rightly dropped it. He was right on the substance of the issue, but that's not enough. It does no good to waste political Capital that could be used on other issues on an issue that has no chance of succeeding.
Trump does not appear willing to accept that reality, and it is unfortunate.
Tell that to the rally attendees.