AMNA NAWAZ: Welcome to the "News Hour."

The director of the Secret Service, Kimberly Cheatle, resigned today, 10 days after a stunning security failure nearly led to the assassination of former President Donald Trump.

Cheatle faced withering bipartisan criticism yesterday for her approach and her lack of answers during testimony before the House Oversight Committee.

We're joined now by Carol Leonnig, investigative reporter for The Washington Post, who's been covering the Secret Service for years.

Carol, welcome back.

And let's just look back.

Given how the last 10 days unfolded and yesterday's hearing, was this resignation inevitable?

CAROL LEONNIG, The Washington Post: You know, the first day of the shooting, I wouldn't have said inevitable, but it became increasingly obvious that she had not just lost the Republicans who were following her, almost chasing her at the RNC, but she had lost the support inside her own agency.

People that I spoke to who were defending her on the night of the shooting and saying, this was a security failure, no question about it, but it can't be totally on her head, they changed their tune and felt very differently.

People who had been her defenders said that her handling of the after-action was her downfall.

In essence, she didn't want to answer questions.

She had not made herself available for press, a press conference, or anybody from the Secret Service that would be available at a press conference the night of the first assassination attempt on a Secret Service protectee in more than 30 years, and that some of her public statements, Amna, were also embarrassing to the agency.

AMNA NAWAZ: Carol, 10 days out from that attempted assassination attempt of a former president, is it any more clear now what could have been done or should have been done to prevent that from happening, where the failures were?

CAROL LEONNIG: You know, the most important failure was line of sight.

In fact, the Secret Service literally has a code in every Secret Service advance plan for an event, LOS.

Line of sight is what the Secret Service is most fearful about in any outdoor or major large event, because - - why?

Because John F. Kennedy was assassinated from a tall building with a long gun in Dallas as he drove in his motorcade.

And those buildings around the motorcade route had not been secured.

Nobody had checked to see, was there a gunman on high?

Well, ever since 1963, and that tragedy for America, the Secret Service has spent oodles of time, endless energy researching, securing, locking down any space that could be on high ground and could shoot at the president, or, in this case, the former president.

And that failure is essential.

The second failure appears to be somewhere in the outer perimeter, the way in which the Secret Service advised, instructed, or created a security plan for local police on that outer perimeter outside the rally, because some communication breakdown occurred.

Between the time an hour before the rally got started, before Trump took the stage, local police had flagged Thomas Matthew Crooks, the gunman, as acting suspiciously, and later flagged him again as a person with a range finder.

This is not a place where people are looking for their golf ball or looking for birds.

But he had a range finder that's often used by shooters to identify a target.

And, somehow, those warnings, though some did get to the Secret Service, didn't result in this individual being detected and sort of locked down and stopped.

AMNA NAWAZ: Carol, I have got about 30 seconds left, but I have to ask you.

There's an acting director now in the form of a 24-year veteran named Ronald Rowe.

Is he any better positioned to make sure this kind of attack doesn't happen again?

CAROL LEONNIG: Ron Rowe has a lot of accolades behind him from agents that I have spoken to, and not just today, but in the 10 years that I have been writing about the Secret Service.

A lot of people feel very solid about him and his experience.

But the challenge he faces is the same one Cheatle faced, which is, this is a agency with less than $3 billion in its budget, limited hiring caps, and an increasingly expanding mission.

They're stretched too thin, something we wrote about 10 years ago, Amna, and something that the Secret Service identified itself and that a blue-ribbon panel identified 10 years ago and that a House Oversight Committee identified 10 years ago.

That stretched-too-thin feature is something that has to be addressed by Congress and by the president today and the president next year.

AMNA NAWAZ: Carol Leonnig of The Washington Post.

Carol, thank you for your reporting and for joining us.

Appreciate it.

CAROL LEONNIG: Of course.