That would be true to the extent that undecideds were dispersed evenly geographically. To the extent they clustered in reachable media markets, you would probably see less decisive areas getting more attention. Personally, I think most forms of campaign effort serves more to reinforce people inclined to vote for you anyway. I can't recall ever seeing a political ad, negative of positive, that actually changed my mind about a candidate. Most campaign rallies or events seem to me to be aimed at reinforcing the commitment of supporters than gaining new ones.
I do agree there is a possibility of a Trump impeachment or 25th Amendment ouster, especially if the Republicans endure the kind of midterm beating the Democrats took under Obama.