As much as people might think the Khan row is an uncalculated knee-jerk reaction from Trump, one which Trump supporters enjoy but the media and the left hate, it's a very well-calculated campaign strategy.
Much in the same way that Trump went directly after Ted Cruz when his PAC made the Melania Ad,
Trump is disabling the power of surrogates and proxy PACs by pulling no punches.
Trump is sending the message, "if you want to speak personally ill of me, at the direction of Hillary, I will make you part of my dialogue against Hillary just the same." There will be no casual toe-dippers in this race. "If you want to get involved in personally smearing me, or pushing dishonest Democratic talking points, I will make you involved in the whole media circus." This makes all but the strongest of political voices of the left question their willingness to get involved in trying to directly attack Trump. Just today, the Khans have said that they want to bow out and quit being involved with this process and the media craziness.
This also takes power away from the DNC and Hillary to start proxy wars against Trump via PACs. Much in the same way that Trump attacked Cruz when his PAC attacked Melania, Trump doesn't care. You'll watch this fall as Trump equates surrogate and PAC messages as though they are direct from Hillary's campaign office. It takes away the delegation power of being able to let crazed/untruthful narratives about your opponent be safely launched away from your pristine camp - to allow you to take some sort of "high road." By going after Hillary for their PAC/surrogate messages, the public will perceive them all as one in the same.Therefore forcing Hillary to comment on these untruths and nasty ads, making them look foolish.
This will also make Hillary less likely to use any radical messages or untruthful ads if her campaign knows that Trump will comment on all of them - equating them directly to her and making her look bad. They will have to be responsible for their message.
By blurring the lines between PAC/surrogate and the candidate, Trump will also be playing on everyone's intuition at this point. We all know that the DNC pays people to spread their message. So who are they trying to fool by wasting money on PACs? We all know they control them in one way or another.