At least some of the source for Donald Trump's struggles on the campaign trail can be traced to this line from his convention address: "I alone can fix" the problems facing the country.
Leaving aside the ideological implications of this line, it reveals the tendency of the Trump campaign to fixate on the persona of the candidate. In its media strategy, the campaign often seems to have the goal not be pounding home some policy message or rallying the troops for races up and down the ticket but instead grabbing headlines for Donald Trump. Over this past week, for instance, rather than focusing on the economic policy laid out in Detroit, he instead has pivoted to throwing rhetorical bombs. As Rich Lowry noted the other day in Politico, Trump has been following a strategy of personality-driven media saturation that could help a media figure solidify a brand--but might be less helpful in actually winning an election.
In the primary campaign, the strategy of personality-driven media saturation probably helped Trump. It gave his campaign media oxygen, and Trump's combative personality help him gain the support of Republicans alienated by the party establishment. However, now that he's the Republican nominee, getting coverage is not nearly as important; he's guaranteed that coverage by virtue of his position. Of course what he says will be covered--he's a major-party nominee! What's more important now for the campaign is that this coverage advances his long-term electoral interest.
One only has to look at recent political polls to see that this flood-the-zone media strategy has not been effective. In fact, a personality-driven campaign plays in many ways into the hands of Hillary Clinton. Secretary Clinton is running on an extremely left-wing platform, and her personal reputation is marred by scandals. The last thing she wants to do is talk policy or have the spotlight be on her. Her favorability ratings are low, but they are often higher than Donald Trump's. In many ways, the more Donald Trump makes this election about him alone, the better it is for Hillary Clinton.
Moreover, bomb-throwing makes it harder to coordinate with other Republican candidates, who fear associating themselves too much with an unstable campaign. As a result, Trump often finds himself running an isolated campaign, which might work in a primary but is much more problematic in the general election. Contrary to the myths of President Obama and other apologists for presidential absolutism, the president alone can't pass major legislation. There's this thing called Congress that actually has to do that. Without strong support on Congress, a President Trump agenda would not have much hope.
Media messaging is far from the only challenge facing the Trump campaign right now, but it does highlight some of the broader structural challenges facing the campaign: a lack of discipline, a fixation on crude dominance, and a confusion of notoriety with electability.
In a democratic republic, I alone gets you only so far. American electoral politics are a team sport--especially at the level of a presidential campaign. Often, it's not in a candidate's best interest to grab headlines (and it's often not in the president's interest, either). A presidential candidate needs surrogates to help reinforce a policy message. He or she needs the trust of party members running in down-ticket races. A presidential campaign just can't be about celebrating the strengths of a candidate or the perfidy of his or her enemies; it instead also has to talk about the needs, aspirations, and possibilities of the nation as a whole. People might tune into to a TV channel to watch a controversial figure, but they very likely won't vote for him for president.