THE BURNED OVER DISTRICT

You can keep the loophole that allows you to sell trucks with filthy polluting rebuilt engines for less than those with newer cleaner engines.

But there is something unusual about the big rigs sold by the Fitzgeralds: They are equipped with rebuilt diesel engines that do not need to comply with rules on modern emissions controls. That makes them cheaper to operate, but means that they spew 40 to 55 times the air pollution of other new trucks, according to federal estimates, including toxins blamed for asthma, lung cancer and a range of other ailments.

The special treatment for the Fitzgerald trucks is made possible by a loophole in federal law that the Obama administration tried to close, and the Trump administration is now championing. The trucks, originally intended as a way to reuse a relatively new engine and other parts after an accident, became attractive for their ability to evade modern emissions standards and other regulations.

The survival of this loophole is a story of money, politics and suspected academic misconduct, according to interviews and government and private documents, and has been facilitated by Scott Pruitt, the administrator of the Environmental Protection Agency, who has staked out positions in environmental fights that benefit the Trump administration’s corporate backers.

The loophole has been condemned in recent weeks by an array of businesses and environmentalists: major truck makers like Volvo and Navistar; fleet owners like the United Parcel Service; lobbying powerhouses like the National Association of Manufacturers; health and environmental groups like the American Lung Association and the Consumer Federation of America; and some Fitzgerald competitors in Tennessee, Texas and Oklahoma, Mr. Pruitt’s home state.

“This just does not make any sense to me,” said Christine Todd Whitman, who served as head of the E.P.A. during the first George W. Bush administration. “Everybody breathes the same air, Democrats or Republicans. It does not matter. This is about keeping people healthy.”

But the Fitzgerald family has had influential allies. In addition to Mr. Pruitt, they include Representative Diane Black, a Republican who is a candidate for Tennessee governor, and Tennessee Technological University, a state university that produced a study minimizing pollution problems associated with the trucks.

Ms. Black introduced legislation in 2015 to protect the loophole when it was first in line to be eliminated by a stricter diesel emissions rule under the Obama administration. That bill failed, but after the election of Mr. Trump, she turned to Mr. Pruitt to carve out an exemption to the new rule — scheduled to take effect last month — and presented him with the study from Tennessee Tech.

Fitzgerald had not only paid for the study, which has roiled the faculty at Tennessee Tech and is the subject of an internal investigation, but it had also offered to build a new research center for the university on land owned by the company. And in the six weeks before Mr. Pruitt announced in November that he would grant the exemption, Fitzgerald business entities, executives and family members contributed at least $225,000 to Ms. Black’s campaign for governor, campaign disclosure records show.

The multiple donors allowed the company to circumvent a Tennessee state law intended to limit the size of campaign contributions by corporations and political action committees. The donations — many of which came through a series of limited liability companies tied to the family — represented 12 percent of the money Ms. Black had raised from outside sources through last month, the records show.

Tommy Fitzgerald, an owner of Fitzgerald, said the actions by Ms. Black and Mr. Pruitt were good public policy and not special favors to his company.

It is said that you have to spend money to make money but you also need people shameless enough to do what you want in return. But just don't think of it as bribery.