The Trump statements were clearly sarcasm, not to be taken seriously. Therefore, a reasonable response from the Democrats and the press might have been - "OK, we know you can deflect attention from yourself so that no one can see how little you know or understand about the workings of our government and the global community. We see how deft you are at making accusations about your opponents that are so outrageous that they clear the room of intelligent conversation.
And how you accuse some reporters of favoring your opponent- "Be quiet - I know you wanna, you know, save her." (See how easy it is to deflect attention from answering a relevant question by hurling an accusation at a reporter.)
Let's see if the Democratic strategists catch on any time soon. By focusing on the Trump sarcasm and treating it seriously, they exhibited muddled thinking, which puts them in a bad position to call Trump out on his muddled thinking, even with the important distinction between being muddled about campaign strategy versus being muddled about international policy. We can look back to the example of Jeb Bush, whose best shot was "You can't bully your way to the presidency, Donald". Oh yes he can if no one figures out how to expose him. A starting point would be to work with calling him out more directly on his modus operandi - "Donald, everything you say amounts to - deny, accuse, deflect, distract, ignore. You can bully your way past the issues during a campaign because the press struggles to deal with you due to their constrictions around being "fair and balanced" to appear objective, but people need to think about what it is like to have a President who does not know anything about our government and our institutions."