New York Gov. Andrew Cuomo described the bombing in Manhattan on Saturday night as "obviously an act of terrorism" even without evidence of the attacker's motive.
But the city's mayor, Bill de Blasio, hesitated at first to use that label.
On Sunday, with the perpetrator still on the loose, he called the bombing "an intentional act" and "a very bad incident" but said there was no evidence of a connection to a terrorist group. "To understand any specific motivation, political motivations, any connection to an organization, that's what we don't know," he said.
His reluctance to use the word "terrorism" quickly became fodder for Donald Trump supporters to criticize Democrats for political correctness and weakness in taking on the country's enemies. The Republican presidential nominee has criticized President Obama for avoiding the term "radical Islamic terrorism," arguing that acknowledging the problem is the first step to combating it.
But determining whether an attack is terrorism can be far from simple.
Federal law defines terrorism as an intentional act that endangers life and is designed to coerce or intimidate the population, influence government policy or affect the conduct of the government. In other words, for an attack to qualify as terrorism, it has to be more than just terrifying. It requires a broader political motive.
By that definition, De Blasio had a point.
The bombing, which occurred in the neighborhood of Chelsea, injured 29 people and spread fear. But in the immediate aftermath, before there was a suspect, it was difficult to say much with any certainty.
"How is someone rational supposed to call it 'terrorism' without knowing who did it, let alone their motive???" tweeted Glenn Greenwald, the journalist and lawyer who has reported extensively on U.S. and British surveillance.
Even Monday, after Ahmad Khan Rahami, 28, was identified as a suspect and taken into custody, it was unclear whether he drew inspiration from a foreign terrorist group, had direct links with such a group or had some other motive. Investigators said there was no evidence that he was part of a broader terrorist cell.
This year, when the Los Angeles Times used government and police reports, terrorism databases, news accounts and independent reporting to compile the worldwide toll of terrorism deaths in the month of April, classifying violence sometimes proved difficult.
In some cases, there was simply not enough information to say that a killing wasn't something other than terrorism — a personal dispute or the work of criminals who aren't motivated by ideology.
In the clearest examples of terrorism, an attacker leave little doubt about motive.
Other instances are fuzzier. Mohamed Lahouaiej Bouhlel, the attacker who killed 84 people with a truck in the French city of Nice in July, had developed a fascination with Islamic State, French prosecutors have said. But they haven't found evidence that he pledged allegiance to the group.
Then there are instances when a terrorist group claims acts of violence when the perpetrators have left it unclear. Such was the case Saturday night at a Minnesota shopping mall, where Dahir Adan stabbed nine people before he was shot dead by an off-duty police officer. Adan was a "soldier of the Islamic State," according to Amaq, the group's news agency.
It is not the first time the organization has used that term to describe so-called lone wolves who were perhaps inspired by the group but have no direct connection.
What is clear is that the use of the word "terrorism" has become highly political.
"Is President Obama going to finally mention the words radical Islamic terrorism?" Trump tweeted after the Orlando massacre.
Obama avoids that language, instead saying that America is at war with "people who have perverted Islam," and that Islamic State isn't representative of Islam.
In December, Clinton seemed to agree, telling a television interviewer that using the term made it sound "like we are declaring war against a religion."
Days after the Orlando attack, however, she altered course. "To me, radical jihadism, radical Islamism, I think they mean the same thing. I'm happy to say either," she said in an NBC interview.
Campaigning Monday, Clinton and Trump accused each other of worsening the threat of future terrorist attacks.
Trump said Clinton's "weakness" had emboldened international terrorists.
Clinton said that Trump's rhetoric made it easier for Islamic State to recruit followers but that he had no plan to defeat the group.
Some analysts saw De Blasio's caution in labeling the New York attack as a boost to Trump's campaign.
"If Trump wins the election, a persistent resistance to calling terrorism terrorism will be a major reason why," tweeted the politics editor at the National Journal, Josh Kraushaar.
By Monday, De Blasio had changed his take. That morning, he edged closer to using the word "terrorism," telling ABC's "Good Morning America": "It's definitely leaning in that direction, the more we know."
At a news conference later in the day, he said, "We have every reason to believe this was an act of terror."