Maryland Sen. Ben Cardin said Tuesday that he has “major concerns” about President-elect Donald Trump’s choice to head the U.S. Environmental Protection Agency after quizzing him about his attitudes towards federal enforcement of the Chesapeake Bay pollution diet, climate change, and other issues.

The two-term Democrat said he met with Oklahoma Attorney General Scott Pruitt in advance of his confirmation hearing before the Senate Environment and Public Works Committee to become the next EPA administrator. The session has not been scheduled yet, but is considered likely next week.

Cardin, a longtime advocate for the Bay cleanup, said he had a “positive” discussion with Pruitt about the Bay, though he remained confused about Pruitt’s rationale for joining a legal challenge to EPA’s imposition in 2010 of a pollution reduction plan for the Chesapeake.

Pruitt was one of 22 state attorneys general to sign an amicus or “friend-of-the-court” brief opposing EPA’s authority to require nutrient and sediment pollution cuts throughout the six-state Chesapeake watershed. The U.S. Supreme Court chose last year not to hear the challenge brought by the American Farm Bureau Federation, the National Association of Home Builders and others.

Their lawsuit had contended that EPA usurped the states’ authority to decide how to clean up the Bay, but lower courts had found the federal agency’s actions were within the law.

Meeting with reporters on Capitol Hill after his interview with Pruitt, Cardin recalled that all of the states in the Bay watershed had participated in development of the binding Baywide pollution reduction plan, known as a “total maximum daily load.”

“He obviously had some concerns about it initially, but he did not discount the federal role in enforcing a regional type compact,” Cardin said.

Still, Cardin said he had to wonder, based on Pruitt’s record, how involved EPA would be under him in pursuing the Bay cleanup.

“I can’t tell you he gave me a sense that he would be an active partner,” Cardin told reporters. “But he was willing to listen. But from what I know about him, I don’t see the type of understanding on the role of federal government in really being aggressive and making sure we carry out our commitments.”

Later, in a telephone interview, Cardin said he “didn’t quite follow” Pruitt’s explanation for joining the legal challenge of the Bay pollution diet. Cardin said Pruitt seemed concerned about the process of federal enforcement, but that he expressed interest in helping the Bay.

Cardin said he tried to sound Pruitt out about energy policy and the role carbon emissions play in climate change, but didn’t get very far. He repeated that he was troubled by the choice of Pruitt to head the EPA when the Republican attorney general from Oklahoma had filed so many lawsuits challenging the very agency he is supposed to lead.

The Maryland senator had issued a statement in early December when Trump tapped Pruitt saying that he would “strongly dispute any nominee who denies the sum of empirical science and the very existence of climate change.”

Cardin said he would wait to hear more from Pruitt at the hearing, but warned the nominee faces “an uphill battle to win my support.”

“I must be candid,” Cardin said. “I don’t think today’s conversation has alleviated my concerns, but it is the beginning of the process and I will certainly be listening at the hearing. But I want to make sure that the person I can support for the Environmental Protection Agency is a person who believes in the mission of the Environmental Protection Agency. And what I’ve seen so far leaves me with major concerns.”