The Trump campaign insists to PBS (as it has for a while) that it is taking a New Approach™ to how campaigns are run. Take, for example, the buses the campaign has in Florida, what it calls "mobile field offices." The campaign's Karen Giorno offered some nice spin: "Politicians take voters for granted, and the idea [of campaign offices] is the old guard, which Hillary represents. That the voter comes to them. We are not the old guard, Mr. Trump wants to go to the voters."
Weirdly, that's entirely backward. Putting a campaign office on a bus may mean that you can drive around to a bunch of voters, but it also means you're only talking to them once — and probably not talking to all of the people you'd need to. Having a campaign office planted in a particular area isn't done so that people can swing by if they want to hear your pitch; it's done so that volunteers can come to a central place and then blanket a certain area over and over. Voters who aren't home will be home some weekend. On Election Day, you have a force of people who know neighborhoods well and who can make sure that targeted voters go to the polls.
It's hard to emphasize enough how important that latter point is for Trump. Usually, Republicans can depend on an older voting bloc that reliably votes. Trump has pinned his hopes on working-class white men, a group that is much less likely to vote. College-educated white women are much more likely to go to the polls — and they prefer Clinton.
During the primaries, Trump had an odd strategy of spending resources on people who rarely vote, which is ill-advised because those people rarely vote. If he wants to turn out people who vote sporadically, he needs to do better than hope they're around the day the Trump bus comes to town.
What's more, Trump's campaign has previously said it would leave the field efforts to the Republican Party. It's not clear which of the offices PBS tallied are led by the GOP, but it does have 18 offices in Wisconsin, for example, which would explain why Trump has 22 offices there. (The RealClearPolitics polling average in Wisconsin has Clinton up by 12; Trump's never done better in polling in the state than trailing by 4.) If the GOP decides in October that knocking on doors for Donald Trump isn't worth their time and money (like in Wisconsin), they don't have to do it. Trump leaving his field outreach to the party is like moving in with a girlfriend you fight with a lot and not getting your name on the lease: You'd better hope you stay in love.
At the same time, NBC News reports that Trump continues to be outspent by Clinton on television advertising. The most recent numbers indicate that Clinton's campaign has spent more than $68 million, paired with nearly $46 million from PACs supporting her. Trump and PACs backing his candidacy have spent about $19 million combined — a figure that Clinton had already matched by the Fourth of July.
It's been clear for some time that Trump believed that the strategy he used to win the primaries — leverage popularity to build a core of support that can outlast a splintered competition — would carry him to victory in November. It was never going to, but it's taken him a long time to figure that out (assuming he has).
If everything written above were being written in May, right after he clinched the nomination: No big deal. Plenty of time. But the election is in 70 days, and Trump is just starting to put together a campaign.