Independent voters are bandwagon voters. They are witnessing all of this enthusiasm for Trump - the parades, the rallies, etc. and many of them will vote for Trump.
If every Republican would have just ran as constitutional conservatives, there wouldn't be a Democrat Party today. There would be a conservative Christian wing of the GOP vs the populist libertarian wing.
That was the entire purpose of the Bush League Republicans (Democrats in R jerseys).
Capture the other party and only give the voters Democrat-lite alternatives.