One should always be wary about blowing a news cycle out of proportion, and, in this crazy primary season, it can be hard to tell what exactly counts as "winning" a news cycle. Still, the past week or so has revealed some potential obstacles for the Trump campaign. Even Ann Coulter has some doubts about the Trump Train's current trajectory.
One of the biggest challenges facing the Trump campaign right now is shifting from an insurgency campaign to a consensus one. The tactics that might have worked earlier in the campaign--such as rhetorical hand-to-hand combat and a reliance on broad slogans--may reach a point of diminishing returns later on. Trump's job is now not to distinguish himself in a pack of seventeen candidates. Instead, it's to unite the party behind him in order to have a good chance in the general election.
Polarizing personal attacks and a lack of policy fluency make that enterprise of unification much harder. General-election voters will be looking for a candidate who seems to have a presidential temperament, and many Republican voters on the fence about Trump have doubts about his public persona. If Trump can't get the support of every Republican, his candidacy can survive, but he faces a much bigger problem if a huge portion of GOP voters refuses to support him.
An inability to forge a broad consensus will harm his quest for the GOP nomination--and the presidency--in multiple ways. If he can't convince many in the party and conservative establishments that he has a reasonable shot at being a successful nominee, he risks collapsing on the second ballot in Cleveland. Furthermore, if his campaign doesn't organize effectively for delegates in various states, many of the delegates pledged to him on the first ballot will be very hostile to him on later ones. The only guaranteed way of avoiding that potential collapse would be to win the nomination on the first ballot with over 1237 pledged delegates going into the convention.
However, his path to 1237 probably requires him to achieve a consensus among Republican voters. To win a majority of delegates, Trump probably has to win by significant margins in many of the outstanding states (few of which are winner-take-all). If he squeaks by with margins of a couple of points in most of these states, he will have a hard time getting enough delegates to arrive at a majority. And, without a majority and a party consensus, he could lose in Cleveland.
Even if Trump were somehow able to win the GOP nomination without a consensus across the right, a fractured Republican party could also spell doom for his chances in the general election. So achieving a consensus would be important for his campaign in both the primary and the general.
The current trend in Wisconsin exemplifies the danger Trump faces. No poll taken over the past couple weeks has shown him with a significant lead, and Ted Cruz's strength in the state has grown considerably throughout March. In fact, numerous polls have shown Cruz with a lead. If Trump can't regain the momentum, Cruz could win the state and get a significant portion of its delegates--delegates Trump will need if he hopes to reach 1237. Trump might have a strong shot of racking up large delegate numbers in states like New York, but many other states (such as California) seem much more in play.
If Trump can't start to do more to build bridges within the right, he'll have a hard time seizing the nomination and occupying the Oval Office. That bridge-building will require more policy sophistication and rhetorical discipline.