Editor’s Note: Julian Zelizer is a professor of history and public affairs at Princeton University and a New America fellow. He is the author of “Jimmy Carter” and “The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society.” The opinions expressed in this commentary are his.

Story highlights

Trump's dominance in New York doesn't erase some of the big challenges he faces, Julian Zelizer says

Trump faces questions over his organization, his rallies and the narrative of his business success, Zelizer says

CNN  — 

With his win in the New York primary, Donald Trump gains the bounce he needs after a rough two weeks filled with disappointing delegate counts and negative media coverage. While it’s not a surprise that Trump does well in his home state, a victory is surely welcome in his headquarters.

Yet even with a big victory, and the delegates that he takes with him, the road ahead will be rough. After several months in which Trump seemed impervious to any kind of attack, his weaknesses have started to become exposed and the strategy for a serious challenge at the convention is becoming clear.

So where are his soft spots?

Organization:

Organization has always been an Achilles heel for the Trump campaign. Though he has hired political guru Paul Manafort to assist with the delegate count, Trump has an enormous amount of catching up to do. He has never taken the organizational grunt work very seriously. He has relied on a media-based strategy that left the ground game for other campaigns.

But right now the costs are becoming clear. As the delegates are selected in different states, Ted Cruz, who has put together a formidable organizational process, is mounting challenges. In Colorado, the Cruz campaign won all of the state’s 34 delegates after Trump won the state earlier in the year. Trump also lost delegates in Iowa, Michigan and South Carolina. This weekend Cruz won at least 50 delegates in Georgia, Wyoming, South Carolina, Kansas and Florida. “This weekend was another delegate bloodbath for Donald Trump,” wrote Kyle Cheney and Katie Glueck in Politico.

The Trump campaign has repeatedly been missing deadlines for candidates to apply to be delegates, leaving the field open for Cruz and his supporters. These kinds of battles will continue in the coming months. The same kind of organizational battles will be even more formidable at the convention. “We are very blessed,” said Ken Cuccinelli of the Cruz campaign, “that our opponent had no idea what he was doing on this until about a month ago.”

Trump might argue that these organizational battles subvert the democratic process (“I win a state in votes and then get nonrepresentative delegates because they are offered all sorts of goodies by Cruz campaign. Bad system!” he tweeted), but the truth is these votes are being won based on the party rules.

Trump can complain all he wants but the reality is that he will need to round up the delegates’ votes if he can’t attain the 1,237 needed for nomination at the Cleveland convention. In the second round of voting at a brokered convention, when delegates are no longer bound to the vote of their state, he might see his support disappear. Organizing might not be as glamorous as the rallies and television appearances but even in this modern day it still matters. Lose that and the nomination might be gone.

Confrontations:

Few things have caused as many questions as the outbreaks of violence at Trump’s rallies. After Iowa the first real pause in the campaign took place after one of his supporters, John McGraw, sucker-punched a protester during a rally in North Carolina. Trump responded, not by condemning the action, but initially offering to pay his bills. On March 19, his campaign manager, Corey Lewandowski, was accused of assaulting a reporter. The charges were dropped but the questions about his supporters remain.

The context of the violence takes place within Trump’s remarks where he talks about physical responses to protesters and makes references to the kinds of actions that we have seen. When asked about a brokered convention, he said, “I think you’d have riots.” Roger Stone, the master of dirty politics and a self-proclaimed friend of Trump, threatened to give out the location of the hotel rooms of anti-Trump delegates so his supporters could exert pressure.

More than anything the violence fuels the perception that Trump is dangerous as a leader and that he is someone who can’t be trusted with the responsibilities of leading a country. It is unclear why Trump has not been more forceful in condemning these actions and avoiding the kind of incendiary language that has caused criticism. Trump has said, “there’s no violence, nobody’s been hurt.”

By failing to condemn the violence, he has not helped his cause and placed into the hands of his opponents a source of damning criticism that they were eager to obtain. Since the reports of violence, Trump’s national poll numbers have been falling.

The Narrative:

Trump has built his entire campaign around a pretty clear narrative: He is a winner, a businessman who knows how to make deals and make money. He will do the same for the country.

While opponents have struggled to find different ways to attack him — castigating his flip-flops, questioning his conservatism, or raising questions about his flamboyant personal background — at the heart of any successful attack will be to undercut the main narrative that he has put forward.

This has been the main lesson of recent campaigns – the best way to defeat an opponent is by discrediting the main story that they have about their campaigns. President George W. Bush’s guru Karl Rove said that attacking the strength of a candidate was the way to defeat him or her.

In 2012, Newt Gingrich in the primaries and then President Obama in the general election ripped apart Mitt Romney’s record as a business person, the centerpiece of his campaign, painting him as a ruthless investor who left broken communities and failed industry wherever he went.

In 2004, President Bush did this to John Kerry, taking the Massachusetts senator’s story of himself as a war hero and falsely crafting perceptions of him as a lying anti-war activist who didn’t really have a military record of accomplishment.

Some of the stories about Trump have come under challenge. With every loss in primaries and caucuses, Trump’s invincibility comes under question. A barrage of negative attack ads from the anti-Trump movement (which the New York Times estimates have cost $70 million ) are starting to take a toll.

While Trump strikes back by accusing Cruz of lying and cheating, some of his shine has worn off. There have also been a growing number of reports that raise questions about Trump’s entire record as a businessman.

As Michael Calderone wrote in The Huffington Post, “Trump’s business dealings — complete with multiple casino bankruptcies, failed branding ventures, employment of undocumented immigrants, long-reported ties to mob-run business and the promotion of a real estate training program that’s now the target of a $40 million fraud suit — has received less sustained coverage this election cycle than his countless Twitter spats, outrageous remarks, and rank bigotry.”

Rather than a list of accomplishments some journalists have been discovering a trail of bankruptcies, failures and financial insecurity. In the coming weeks, those attacks will certainly intensify and Trump will have to work hard to make sure that his story of being a winner in business does not come undone going into California.

It would be a big mistake to count Trump out or to assume that Ted Cruz and John Kasich will be able to exploit any of these vulnerabilities all the way to victory. He has outsmarted his critics throughout this campaign. Once he was the person who could never win the nomination, now the discussion is whether he can win the general election.

Apparently recognizing some of his vulnerabilities, Trump has remained relatively quiet during the past few weeks, even meeting with Megyn Kelly. He’s attempted to soften some of the controversy about his campaign and present a more stable image.

But that doesn’t mean he can’t be defeated and that he has not been politically wounded. During the past few weeks, he has shown where the points of weakness are. If he’s not more cautious and if he doesn’t start making changes, he might find a campaign that was on the cusp of victory find itself in the throes of defeat.

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Julian Zelizer is a professor of history and public affairs at Princeton University and a New America fellow. He is the author of “Jimmy Carter” and “The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society.” The opinions expressed in this commentary are his.