It might be via an ad as deadly as the LBJ ad that sunk Barry Goldwater:
Glenn Kessler explains here.
Trump should really stop responding to each of these attacks or libertarian fanboys are going to quickly learn the limits of Trump's skill in taking apart the establishment.
Trump should really be taking Robert Ringer's advice, but it doesn't seem to be in his chemistry,
He bizarrely seems to double down on lies and bring focus on them. That's not going to work against the skilled communication hit artists that Hillary employs and the willing establishment media to emphasize the Hillary hit team messages. Trump will have to hit Hillary very hard just to survive.