GEOFF BENNETT: President Trump's efforts to overhaul the Environmental Protection Agency are being cheered by many in the fossil fuel industry who are critics of what they say is excessive regulation.

But many, including scientists and environmentalists, are deeply concerned.

Our William Brangham joins us now with more -- William.

WILLIAM BRANGHAM: Geoff, the EPA's new administrator, Lee Zeldin, has been quite explicit, saying he is -- quote -- "driving a dagger through the heart of climate change religion."

That has meant enormous changes, ranging from laying off EPA scientists, repealing dozens of rules and regulations, to challenging the very idea that greenhouse gases endanger human health.

We are joined now by two former EPA administrators.

Christine Todd Whitman headed the agency under President George W. Bush and is a former Republican governor of New Jersey.

And Gina McCarthy ran the EPA under President Obama and served as a top climate adviser to President Biden.

Thank you both so much for being here.

Christine Todd Whitman, to you first.

You and Gina McCarthy have both been -- excuse me.

Gina McCarthy, excuse me, to you first.

You and Christine Todd Whitman have both very clear about the dismay that you see at what is happening at the agency that you used to run.

When you look at the scale and scope of what is going on, what is it that most stands out to you?

GINA MCCARTHY, Former Administrator, Environmental Protection Agency: Well, first of all, I thank Christie for all of her work, and Bill Reilly as well.

We put out an op-ed just a few weeks ago on this.

Look, they are challenging all of the fundamental tenets of what EPA stands for.

First of all, we know that Administrator Leavitt (sic) has changed the mission of the agency from protecting health and the environment to American energy dominance.

Now, how does that work for an agency that's trying to people healthy, that's trying to reduce sources of pollution, and do it in a way that's credible and consistent with the laws of our country?

And so it is a sad moment right now, because they're trying to dismiss 65 percent of the human beings that have worked so hard at EPA.

And they're really looking at dismantling all of the scientists, the Office of Research and Development, our Environmental Justice office.

So there is nothing that isn't at risk at EPA, but, most importantly, the risk it poses to people in our country is extraordinary, and they have to be aware, because we may end up having to protect ourselves if EPA isn't there for us.

WILLIAM BRANGHAM: Christine Todd Whitman, one of the things that Gina McCarthy just mentioned was the potential dismissal of a series of scientists, including those at the Office for Research and Development.

For people who don't know, can you explain who those people are and what their dismissal or departure would mean for the agency?

CHRISTINE TODD WHITMAN, Former Administrator, Environmental Protection Agency: Well, what it means is, you basically stopped doing research on new and potential problems for the public, for public health.

I mean, these are the people that have done all the research on plastics, showing how microorganisms or micro pieces of the plastic are now getting into the human food chain, and why it's important that we start to deal with that.

These are the people that are looking ahead.

I mean, when we had the anthrax attacks, there was no standard for what was safe, one spore of anthrax, 15 spores of anthrax.

That came back to us.

It was the EPA that set the standard.

We set it at zero.

But the scientists followed that up to see, what is the safe standard?

So these are people who are working every day to protect us and to look for new areas where we might have problems or things that we have seen as problematic in the past that are not so problematic now, that we figured out ways around them or they're not as bad as we thought they might have been.

EPA has a very simple mission, as I'm sure Gina said, which is to protect human health and the environment.

And these scientists are focused on doing just that, on making sure that we anticipate where there may be problems and to address them as quickly as we can with -- based on science, emissions from cars, lead in pipes that gets into the drinking water.

EPA is the one who did the research to show the impact on children's health and development, brain development, from lead in pipes and passed the regulations to reduce that.

So it really has -- and these scientists are the ones that have a very real impact on people's everyday lives.

WILLIAM BRANGHAM: Gina McCarthy, President Trump, when he was a candidate, was crystal clear how he stood.

He thought that climate change is not something to focus on.

He said regulations, including those from the EPA, are hurting consumers,they are hurting the economy.

He's clearly got a big constituency in the business community that agrees with him on a lot of those points.

And he won the election.

Is that not how democracy is supposed to work?

GINA MCCARTHY: No, that's not how democracy is supposed to work.

I mean, the president can have his opinions, but EPA is regulated by Congress.

They establish laws.

EPA is required under the law to implement the actions that Congress is demanding.

And EPA has been doing that.

But I think the bigger challenge is, let's not lose sight of the fact that the federal government is really falling apart in so many ways.

EPA is definitely one of the targets.

But, rest assured, we have to rally the troops in states and local communities.

And, frankly, that's where I'm spending most of my time actually working with Bloomberg on America is All In, because states also have legal authority.

So we have to move forward and protect the interests of people in this country and protect our natural resources.

And if the federal government wants to drop that charge, then the rest of the country is going to pick it up.

And that's what we're working on now.

And it is an enormous coalition that continues to grow.

That includes businesses and institutions as well.

So this is not just about states and local governments.

It's about all of us trying to protect our interests of our children in which climate change is concerned, protect our ability to live healthy lives and leave our children in a better position than we are in right now.

WILLIAM BRANGHAM: Christine Whitman, the -- in 2009, on this, specifically on this issue of climate change, in 2009, EPA said carbon dioxide and greenhouse gases are a direct threat to human health.

That funding -- that finding has now allowed EPA to take a lot of action to combat the negative effects of climate change.

The current EPA administrator, Zeldin, says he wants to look at that finding again and potentially undo it.

What would that do to the EPA's ability to address climate change specifically?

CHRISTINE TODD WHITMAN: Well, it would pull a rug out from under them.

And if we haven't seen from these ever-increasing storms, the severity of the storms, the droughts, the floods, the tornadoes the real economic and human impact of what's going on, we -- you can't deny climate change.

It's happening.

I mean, we're not the cause of it, but we certainly exacerbate what's going on.

And we need to be smart about figuring out, how do we take advantage of new technologies to slow down what's happening, to prepare for the kind of impact that we're seeing around the country, and to do better with everyone?

And nobody does innovation better than the United States.

And that's where we should be focusing.

What can we do to continue to grow our economy, actually to grow it faster?

Because you can't have a healthy economy if people don't have clean water to drink and clean air to breathe and if we don't try to harden ourselves against these ever-increasing storms and disasters that we see around the country.

WILLIAM BRANGHAM: All right, that is Christine Todd Whitman and Gina McCarthy, both former heads of the Environmental Protection Agency.

Thank you both so much for being here.

CHRISTINE TODD WHITMAN: Pleasure.

GINA MCCARTHY: Thanks.

Thanks, Christie.