WITHIN THE space of 12 hours on Saturday, there were explosions in New Jersey and New York and a mass stabbing in Minnesota . Dozens of people were injured, though thankfully no victims were killed in what authorities are investigating as acts of terrorism. No question the events were scary: “This is the nightmare scenario” in a post-9/11 world, said New York Gov. Andrew Cuomo (D). At the same time, Americans should feel reassured by how competently and seamlessly local, state and federal authorities responded to the attacks, prevented others and developed leads.

Even better, ordinary citizens — particularly those in New York and New Jersey who bear the scars of previous attacks — resolved not to give in to fear or panic. Instead, they helped out neighbors in need and got back to their business.

Less than two days after a bomb designed to do maximum damage exploded in the Chelsea neighborhood and other devices were found in New York City and New Jersey, authorities had identified and apprehended a suspect. Ahmad Khan Rahami, 28, a U.S. citizen born in Afghanistan, was taken into custody after an apparent shootout with police in which he was wounded and two police officers were shot.

What motivated him, whether he acted alone or was influenced by or connected to international terrorist groups, will be the focus of the ongoing investigation by multiple agencies. The same kind of questions are being probed in the case of Dahir Aden, the 22-year-old who went on a stabbing rampage in a St. Cloud shopping mall before he was killed by an off-duty police officer. A news agency linked to the Islamic State called him a soldier of the terrorist group, and police said he asked at least one victim whether they were Muslim before assaulting them and referred to Allah ­during the attacks.

In commending law enforcement and counterterrorism officials, President Obama on Monday stressed the importance of letting them do their jobs so as to prevent false reports or incomplete information. The obvious need for such prudence sadly — but not surprisingly — did not seem to matter to Republican presidential nominee Donald Trump. Before there was any determination of the Chelsea explosion’s source, Mr. Trump nonetheless proclaimed at a campaign stop in Colorado that a bomb had gone off. He may have guessed right, but that would be a reckless way to do business in the Oval Office.

Democratic presidential nominee Hillary Clinton said that preventing radicalization is a key part of the war on terror, during a Sept. 19 press conference. (The Washington Post)

Equally disturbing was Mr. Trump’s bombast about how he would approach terrorism — “knock the hell out of ’em” — and maybe use racial profiling. By contrast, Democratic nominee Hillary Clinton wanted to know the facts, and called for the support of first responders and prayers for the injured. It was the kind of calm and caution one naturally expects from a leader.