Environmental Protection Agency Administrator Scott Pruitt appeared, May 16, before a Senate Appropriations subcommittee on the Interior, Environment, and Related Agencies on budget on Capitol Hill in Washington.
Trump tweeted that Pruitt would be replaced by his former deputy at the EPA, Andrew Wheeler, who would serve as acting administrator starting on Monday.
Trump on Thursday said he has confidence that Wheeler "will continue on with our great and lasting EPA agenda". He even told them to contact conservative groups and companies to find a lucrative job for his unemployed wife, including as a Chick-fil-A franchisee.
Mr Pruitt's fate seemed secure for the rest of Wednesday at least, since it was Independence Day and the president had no scheduled public appearances aside from a picnic in the grounds of the White House.
As Oklahoma's attorney general, Pruitt had sued the agency 14 times on behalf of the state challenging a variety of regulations and billing himself as "a leading activist against EPA's activist agenda". Pruitt, who gave every appearance of being in the pocket of industry, spent large portions of his time denying the existence of climate change.
"This man is directly and significantly harming my child's - and every child's - health and future with decisions to roll back environmental regulations for the benefit of big corporations, while he uses taxpayer money to fund a lavish lifestyle", wrote Mink, whose Facebook page identifies her as a high school teacher.
Although Pruitt's exit had always been expected, a member of Pruitt's staff told Newsmax an hour before Trump's tweet that "he's not going anywhere anytime soon".
"Instead of protecting our environment and combating climate change, he has worked to protect the interests of the fossil fuel industry and polluters all over the country", Sen.
Pruitt also rankled some Republican lawmakers, including in Midwest corn states, because of his efforts to overhaul a U.S. policy requiring biofuels like corn-based ethanol in gasoline.
Massachusetts Democrats, who vocally criticized the EPA chief's actions and efforts to reverse Obama-era policies, praised news of Pruitt's resignation.
Here are some things to know about Pruitt's second-in-command, who needs Senate confirmation before he becomes the agency's permanent leader.
They asked the EPA's inspector general, Arthur Elkins, to take appropriate steps to hold Pruitt accountable. Pruitt is the seventh person to leave a Cabinet-level post in the Trump administration.
White House homeland security adviser Tom Bossert resigned in April, a month after Rex Tillerson was sacked as secretary of state.
"This is a restaurant that is very outspoken about being protective of the environment", the manager told the New York Daily News.
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Meanwhile, the White House has used its official Twitter account to attack Democratic Senators Kamala Harris and Elizabeth Warren. If there are elements that work, we can maintain and strengthen those aspects.