WASHINGTON — Republican senators want President Donald Trump’s embattled environmental chief to address questions about ethics and spending decisions, but so far are stopping short of calling for him to step down.

Scott Pruitt’s answers at House hearings Thursday could prove crucial in determining whether he stays atop the Environmental Protection Agency, lawmakers said.

Republicans have largely stood behind Pruitt as he fends off a barrage of ethics troubles, saying they are encouraged by his efforts to ease federal regulations on manufacturing, mining and other industries. But as fresh allegations against Pruitt keep surfacing, Republicans increasingly are raising doubts about his job security.

Sens. John Barrasso, R-Wyo., and John Thune, R-S.D., said Pruitt faces “serious questions” about his use of taxpayer money.

“I want to make sure taxpayers are getting value for their dollars, make sure money is being spent appropriately. So there continue to be serious questions,” said Barrasso, chairman of the Senate Environment and Public Works Committee. “We’ll see what comes out of the hearings on Thursday.”

Even Pruitt’s political mentor, GOP Sen. Jim Inhofe of Oklahoma, called recent allegations about Pruitt “concerning.”

Inhofe said he generally has been pleased with the performance of Pruitt — a former Oklahoma attorney general — in rolling back regulations and “restoring the EPA to its proper size and scope.”

But he said “these latest reports are new to me. While I have no reason to believe they are true, they are concerning and I think we should hear directly from Administrator Pruitt about them.”

While Trump has previously backed Pruitt, White House press secretary Sarah Huckabee Sanders appeared noncommittal on Wednesday. “We’re evaluating these concerns and we expect the EPA administrator to answer for them,” Sanders said.

Administration officials said Pruitt has declined White House help in preparing for Thursday’s hearings, to be held by subcommittees of the House Energy and Commerce and Appropriations panels. Other Cabinet members — including Housing and Urban Development Secretary Ben Carson and Interior Secretary Ryan Zinke — have accepted White House help in similar situations.

While administration officials have cheered Pruitt’s actions to roll back environmental regulations, many have grown weary of the continued allegations against him. Former coal lobbyist Andrew Wheeler was recently confirmed as Pruitt’s deputy, and some Republicans say privately that Wheeler, a former EPA and Inhofe staffer, could continue the agency’s deregulatory agenda without the drama that surrounds Pruitt.

A GOP Senate aide called Wheeler a good choice to lead EPA but said speculation about him was “premature.” The aide spoke on condition of anonymity to discuss internal deliberations.

“Obviously, Scott Pruitt has got some serious questions to answer,” said Thune, the third-ranking Republican in the Senate.

Questions about Pruitt include his use of shell companies in Oklahoma real estate deals and spending taxpayer money for such personal perks as first-class airline seats. The Associated Press and other news media reported this week that EPA’s security chief worked on the side as a private investigator for the owner of a tabloid news company with close ties to Trump.

EPA special agent Pasquale “Nino” Perrotta performed regular work for National Enquirer publisher American Media Inc. during the 2016 election, according to person with knowledge of the company’s internal workings. The person was not authorized to speak publicly about the company’s operations and spoke on condition of anonymity.

In addition to his job at EPA, Perrotta is the top executive at Sequoia Security Group, a Maryland-based security firm.