"I'm concerned that the Trump administration's assault on human health and the environment will continue long past Pruitt's departure from EPA", Pallone said. President Trump tweeted the announcement, saying the agency's deputy administrator will assume the position until the President nominates a new Secretary.
Trump tweeted that he has "no doubt that Andy will continue on with our great and lasting EPA agenda. We have made tremendous progress and the future of the EPA is very bright", Trump wrote.
In his resignation letter, Pruitt cited "the unrelenting attacks" that were taking a toll on him and his family.
Kaitlyn Schallhorn is a Reporter for Fox News.
Pruitt was at the White House with other cabinet members on Wednesday evening, celebrating the Fourth of July and watching fireworks.
Pruitt was a former Oklahoma attorney general who filed a number of lawsuits against the EPA, according to the agency's website.
At the time, the president was feuding with Sessions over the AG's decision to recuse himself from the Russian Federation investigation, according to CNN, which cited three people familiar with Pruitt's pitch.
"From moving to roll back strong fuel economy standards, to repealing the Clean Power Plan, to undermining chemical regulation, to suppressing climate science, to advocating for US withdrawal from the Paris climate agreement, Scott Pruitt made the EPA stand for Every Polluter's Ally", he said in a statement. Like Pruitt, Wheeler is a conservative who will seek to roll back what some see as excessive air and water regulation.
Senator Kamala Harris, Democrat from California:"Just because Scott Pruitt resigned doesn't mean we've forgotten about the taxpayer funds he's misused or the damage he's done to our environment".
Democratic U.S. Representative Gerry Connolly said after his resignation: "Scott Pruitt's reign of venality is finally over". Health and Human Services Secretary Tom Price resigned a year ago after it was reported he spent taxpayer funds on charter flights.
According to The Washington Post, Pruitt pushed to find his wife a well-paying job with a politically connected group. In addition, he was formerly chief of staff to Sen. John Barrasso (R-WY) and James Inhofe (R-OK) - who voted to approve his nomination in February.
"It has become increasingly challenging for the EPA to carry out its mission with the administrator under investigation", said Barrasso, who is from Wyoming.
But where Pruitt came to Washington as an outsider, Wheeler has spent two decades in the nation's capital - making him an experienced insider who knows how to work the system.