Here are the highlights so far:
An opening barrage from Democrats
Representative Paul Tonko, Democrat of New York, asked Mr. Pruitt to say “yes or no” to whether he had approved pay raises for two E.P.A. employees he brought with him from Oklahoma.
Mr. Pruitt said he had delegated the authority to grant such approvals, or as he put it, “There was delegation given in my authority.” He said, “I was not aware of the amount, and I was not aware of the bypassing that was going on.” Mr. Tonko said the answer suggests “you have no idea what is going on” under Mr. Pruitt’s name at the agency.
Representative Frank Pallone Jr., a New Jersey Democrat, was even more direct in his opening remarks. “You are unfit to hold public office and undeserving of the public trust,” he told Mr. Pruitt. “Every indication we have is you really should resign.”
He followed up by asking Mr. Pruitt whether he had sidelined or demoted at least five employees who disagreed with him, demanding a “yes or no” answer as to whether he had called for these changes.
“I don’t ever recall a conversation about that,” Mr. Pruitt said.
“I’ll take that as a yes,” Mr. Pallone responded.
“You shouldn’t take that as a yes,” the administrator pushed back.
Mr. Pallone continued to press. “Has it always been your practice to fire people who disagree with you?”
He then moved on to talk about a toxic chemical that was on track to be banned when action was delayed by the agency under Mr. Pruitt.
Mr. Pruitt responded that the review had not been closed. Mr. Pallone responded that the lack of action on that chemical and others “makes a mockery of the E.P.A.”
A more cordial welcome from Republicans
Republicans also chastised Mr. Pruitt in opening remarks, but their questions tended to be much more gentle.
Representative Joe Barton of Texas, who has long denied the overwhelming evidence of human effects on climate change, offered sympathy. “Mr. Pruitt, you’re not the first victim of Washington politics,” he said.
As to Mr. Pruitt’s penchant for first-class travel, Mr. Barton said: “You’ve been attacked for flying first class. Was that illegal? It may look bad, but it’s not illegal.”
Representative David B. McKinley, Republican of West Virginia, told Mr. Pruitt sympathetically that the attacks on him “have an echo of McCarthyism.”
The phone booth
Representative Diana DeGette, a Colorado Democrat, drilled down on some of the ethics questions concerning Mr. Pruitt’s expenses in office and his past financial dealings.
She first asked about Mr. Pruitt’s famous soundproof booth, installed in his E.P.A. office at a cost of $43,000. The Government Accountability Office has ruled that the expenditure broke the law.
Mr. Pruitt had previously testified that the expense was appropriate. In light of the recent ruling, Ms. DeGette asked whether Mr. Pruitt knew that the purchase had violated the law and whether anyone would be penalized.
“We are investigating this internally,” he said.
“Would you agree that public officials should be held to the highest standards of ethical conduct?” she asked. He responded that he did.
Representative Tony Cárdenas, a California Democrat, also brought up the phone booth.
“I was not aware of the approval of the $43,000,” Mr. Pruitt told him, “and if I had known about it, congressman, I would not have approved it.”
Mr. Cárdenas responded that “if someone was spending $43,000 in my office, I would know about it.”
Representative Anna G. Eshoo, a California Democrat, had scathing criticism for Mr. Pruitt when her turn for questioning came. “You have a solid record of violating ethics rules from the state level to the federal government,” she told him. “I think it’s an embarrassment.”
Then she asked: “Do you have any remorse? Yes or no?”
Mr. Pruitt responded: “I think there are changes I’ve made already. I’ve made a change from first class to coach travel.”
She returned to her call for a yes-or-no answer, and asked Mr. Pruitt whether he would reimburse the government. He launched into a long response, but she cut him off.
“With all due respect, I may be elected, but I’m not a fool,” she said. “This is not ‘dodge-question’ day.”
Oklahoma real estate
Ms. DeGette also questioned Mr. Pruitt about his involvement in real estate deals in Oklahoma, referring to the purchaser of his home as a “shell company.”
“It’s not a shell company,” he said quickly, and said that such financial structures were commonly used to purchase real estate in Oklahoma.
She then asked Mr. Pruitt whether he had paid taxes on rent he received. He said such issues had been handed over to an accountant.
“I’m not doing this to hassle you. I’m doing this as an elected official,” Ms. DeGette said as she ended her questions. “Everything we do has to be to the highest ethical standards.”
When asked about his announcement this week that the E.P.A. would restrict the kinds of scientific studies that it would use in forming policy, Mr. Pruitt responded: “It seems to me that it’s common sense that as we do rule-making, we base it on scientific conclusions that we should be able to see the data and methodology that causes those conclusions. That makes sense to me.”
Tensions with California
Mr. Pruitt said that the agency was “not at present” planning any efforts to revoke a decades-old waiver that allows California to enforce its own emissions standards on automobiles.
But he would not say definitively whether that was a final position. The E.P.A. is “working very diligently and diplomatically with California to find answers on this issue,” Mr. Pruitt said, in response to questions from Representative Doris Matsui, a California Democrat who has sought to protect her state’s ability to regulate emissions.
The White House reaction
It is Mr. Trump’s opinion of the E.P.A. administrator that matters most at the end of the day, and his Twitter account may offer insight into Mr. Pruitt’s fate. Two weeks ago, Mr. Trump tweeted his support of Mr. Pruitt, writing: “While Security spending was somewhat more than his predecessor, Scott Pruitt has received death threats because of his bold actions at EPA. Record clean Air & Water while saving USA Billions of Dollars. Rent was about market rate, travel expenses OK. Scott is doing a great job!”
On Wednesday, Sarah Huckabee Sanders, the president’s press secretary, said a White House review of Mr. Pruitt’s ethics issues was “ongoing” but offered no details. “We’re evaluating these concerns and we expect the E.P.A. administrator to answer for them and we’ll keep you posted,” she said.