I don't think it is ever going to happen. Haven't you noticed how the news people always keep him in the lime light. I really think the left has set this all up because they knew Hillary was not going to make it and they knew America was fed up with having another Democrat President (Typically after 8 yrs it goes back to the opposite party) So they have ordained a wolf in sheep's clothing to fool a majority of the people and to get someone they know they can work with. And for that reason they aren't going to go after him.
That way, if they somehow cannot get the republicans knocked off then at least they'll have a president they can 'work with'.
Given the amount of material they must have on Trump that has not yet been hammered in the press (in fact they've barely laid a glove on him, relatively speaking) I suspect they are holding it back until there are no other options available to us.