AMNA NAWAZ: Welcome to the "NewsHour."

Federal investigators say the crew of the train that derailed in East Palestine, Ohio, tried to slow and stop the train after getting a critical sensor warning.

GEOFF BENNETT: But the preliminary investigation also found that warning, which came from an overheated axle, did not arrive until just moments before the train went off the track.

AMNA NAWAZ: Investigators have not determined the cause of the derailment in East Palestine, but today's report from the National Transportation Safety Board, or NTSB, pointed to a key clue, an overheated wheel bearing that was 253 degrees hotter than the air temperature.

Investigators said that set off a sensor and audible warnings on the Norfolk Southern train.

But the temperature did not reach a level that would have required the crew to stop the train by the company's own rules until just before the accident.

JENNIFER HOMENDY, Chair, National Transportation Safety Board: The warning threshold is set by railroads.

And, again, it varies by railroad.

We're going to look at that and see if that threshold should have changed -- should change.

GEOFF BENNETT: Jennifer Homendy is chair of the NTSB.

JENNIFER HOMENDY: I will tell you that, had there been a detector earlier, it would not have -- that derailment may not have occurred.

But that's something we have to look at.

GEOFF BENNETT: The 149-car train derailed nearly three weeks ago.

Its 38 cars came off the tracks, 11 of them tank cars that dumped more than 100,000 gallons of hazardous chemicals, including vinyl chloride, which is linked to cancer.

The EPA says its tests show the air and municipal drinking water in East Palestine are safe.

Today's NTSB report also found the train was traveling 47 miles per hour before the accident, which was below the speed limit.

Residents in East Palestine remain anxious and frustrated about the aftermath.

CRYSTAL MAHONEY, East Palestine, Ohio, Resident: What goes up has to come down.

If it's attaching to this water, where's it going?

How do I protect my family from something I can't see?

GEOFF BENNETT: And they have questioned why Norfolk Southern and authorities opted for a controlled burn of the chemicals.

In its preliminary report, the NTSB said that happened because the temperature in one of the tank cars was very high and could have led to a catastrophic explosion.

The report was released as Transportation Secretary Pete Buttigieg was on the ground in East Palestine today.

He said the accident showed the need for tougher regulation from Congress and higher safety protocols from the rail industry.

PETE BUTTIGIEG, U.S. Secretary of Transportation: Norfolk Southern and the other freight rail companies need to stop fighting us every time we try to do a regulation.

GEOFF BENNETT: He also acknowledged he may have waited too long to travel there, saying he wanted to let the EPA and NTSB deal with the emergency first.

The federal response has become a partisan flash point.

DONALD TRUMP, Former President of the United States: We have told you loud and clear you are not forgotten.

GEOFF BENNETT: Yesterday, Donald Trump visited the area and blasted President Biden for not yet visiting East Palestine.

DONALD TRUMP: They heard I was coming.

They all came.

They weren't going to come.

They were going to leave you abandoned.

And now they're not.

GEOFF BENNETT: Today, Buttigieg pushed back, arguing that the Trump administration eased up on safety regulations too easily to satisfy the railroad companies.

PETE BUTTIGIEG: One thing he could do is express support for reversing the deregulation that happened on his watch.

GEOFF BENNETT: The NTSB said today it will carefully investigate sensors, alarms and the rules set by railroads.

It also plans to hold a rare investigative hearing in East Palestine this spring.