Day by day, we learn more about a growing forest of red flags that alerted federal law enforcement agencies to scrutinize New York bombing suspect Ahmad Rahami.

Among those forehead-slapping clues: Rahami allegedly assembled his bomb-making materials in plain sight — “ordering components on eBay, having them delivered to a New Jersey business where he worked, and even testing some of the material in his family’s backyard,” The Wall Street Journal reports.

There’s a cell phone video of a blast in that backyard, two days before investigators say Rahami put a series of bombs in New York and New Jersey. The video shows a black, partially buried container exploding in flames — “followed by billowing smoke and laughter.”

It’s frustrating that none of these blindingly obvious clues helped the feds avert last weekend’s bombings in New York and New Jersey. The only lucky break in this case is that, miraculously, no one was killed.

Cases like these are particularly unsettling to Americans because suspects aren’t plotting in soundproof, airtight rooms deep underground. They’re going about their terrorist planning chores out in the open.

And in many cases, these suspects come up on the radar of federal authorities. In 2014, Rahami was flagged for federal scrutiny when he returned from a nearly yearlong trip to Pakistan, The New York Times reports. Federal agents examined his travel history and Rahami’s father’s concerns over his son’s increasingly violent behavior.

But federal authorities apparently believed the case merited no deeper scrutiny.

Don’t get us wrong. We’re not second-guessing feds or local police in this case. We’re sure the FBI and other law enforcement agents sift through heaps of similar leads that yield nothing.

The feds can’t surveil everyone who may pose a threat. And they can’t stop every attack. That’s a given. But that’s not a white flag.

In Monday night’s presidential debate, Hillary Clinton and Donald Trump will be asked about the Rahami case and the other terrorist attacks in Europe. Those attacks may be organized and executed by different people, but they’re part of the same Islamic State-inspired terrorism campaign.

We hope to hear more from the candidates about what the U.S. can do to fortify its defenses, and to help its allies abroad. What new ideas do they have to battle this evolving threat?

How would they beef up law enforcement’s ability to detect and thwart attacks? Do they think last year’s congressional restrictions on the government’s sweeping antiterrorism surveillance powers play into this case? Or was there something more basic, more telling, in the failure of the feds to anticipate and intercept this plot before it fully hatched?

Ms. Clinton, Mr. Trump, no more talking points about resolve and revenge.

Monday night, pitch forward.

What would you do?

—The Chicago Tribune