Image copyright Getty Images

Environmental Protection Agency head Scott Pruitt has resigned after months of inquiries into a range of controversies swirling around him.

Here's a run-down of the trouble Mr Pruitt faced, how he tried to explain them and just why they got him in so much hot water.

The bargain room for rent

For $50 a night, a Washington tourist might be lucky to get bare-bones accommodation in a seedy motel in a distant suburb. For that same amount, however, Mr Pruitt landed a room for six months last year in a furnished townhouse just a few blocks from the US Capitol.

Image copyright Getty Images Image caption Scott Pruitt rented a room in this Capitol Hill townhouse for $50 a night

He only paid for nights he stayed there, and his daughter - who was working as a White House intern - had her own room (with no indication of what, if anything, she paid).

The house is owned by the wife of an energy industry lobbyist, and while Mr Pruitt has insisted that there was no potential conflict of interest, that does not appear to be the case.

Mr Pruitt points to an EPA ethics review that approved his lease, but several agency employees involved have since said they were not given all the relevant information.

Hot water temperature: Boiling. Accepting below-market-rate housing from a deep-pocketed Washington lobbyist with business before your agency? It doesn't get much swampier than that.

Sirens to clear the traffic

Early in Mr Pruitt's tenure as EPA chief, he reportedly requested that his motorcade use flashing lights and police sirens to speed trips through Washington-area traffic when he was late for official meetings or rushing to the airport for a flight.

In at least one instance, according to the New York Times, he used it to speed to dinner at a trendy French restaurant.

Per multiple media accounts, the head of Mr Pruitt's protective detail - a 16-year-veteran of the EPA - objected to the use of the sirens and was subsequently reassigned within the agency.

Agency officials have denied that Mr Pruitt requested the sirens or that their use deviated from government guidelines.

Water temperature: Simmering. In the vast scheme of things this is a relatively minor issue, but demanding traffic-halting motorcades to chic French bistros is the kind of tidbit that can capture the public's attention.

The travel budget

In his first year as EPA administrator, Mr Pruitt spent more than $168,000 on air travel across the US, including frequent trips to his home state of Oklahoma and several international journeys. He often relied on charter jet service or first-class commercial airline seats because, per the agency, security concerns prevented him from mingling with the masses in coach.

Image copyright Getty Images Image caption The EPA spent more than $90,000 on Scott Pruitt's travel in June 2017, which included a trip to Italy for an environmental summit

Mr Pruitt spent $36,000 for a military flight from Cincinnati to New York so he could catch a first-class flight to Italy, where he met with foreign leaders and took a private tour of the Vatican.

An EPA spokesperson told the Washington Post that Mr Pruitt's travels have all been approved by the agency and were needed to spread the administration's message and hear "directly from people affected by EPA's regulatory overreach".

Fox News' Lukas Mikelionis notes that previous EPA administrators have spent similar figures on their foreign trips, when factoring in higher costs for Mr Pruitt's round-the-clock security.

Water temperature: Toasty. Extensive use of first-class and charter travel was enough to force Health and Human Services Secretary Tom Price out of his job last year, but travel-scandal fatigue may be setting in. Interior Secretary Ryan Zinke has faced similar allegations and seems secure in his job.

Questionable purchases

Then there are some rather unusual purchases the EPA has made under Mr Pruitt's tenure. His office spent $5,800 on thumb-print security locks, $1560 for 12 fountain pens and $43,000 for a soundproof phone booth. There was a proposal for $70,000 to replace two desks in his office suite, including one that was bulletproof. In the end, however, the EPA ended up spending $2,000 to refurbish an antique oversize desk for Mr Pruitt that was being stored in a government warehouse.

Water temperature: Tepid. Nothing is going to top Housing and Urban Development Secretary Ben Carson's since cancelled purchase of a $30,000 dining set for his office, although bulletproof desks and soundproof communications stations do reveal a bit of an obsession with security.

Misuse of staffers

Last year Mr Pruitt reportedly instructed an aide to contact Republican donors and businesses in an effort to find six-figure employment for his wife, Marlyn. In one notable instance detailed by the Washington Post, the EPA chief had his scheduler reach out to the head of the fast-food company Chick-fil-A to explore the possibility of having his wife operate one of their franchises.

Mrs Pruitt, a former school nurse in Oklahoma, performed consulting work for several clients with Republican ties - involvements that could violate ethics rules prohibiting government officials from using their positions for personal financial gain.

Jobs weren't the only thing Mr Pruitt had staffers hunting for, either. According to congressional testimony, the EPA head instructed his aides to find a new apartment for him, call the Trump hotel to inquire about purchasing a used mattress, buy him fancy snack food, arrange a family vacation to California, pick up his dry cleaning and search for a particular brand of moisturising lotion available only in select Ritz-Carlton hotels.

On multiple occasions staffers reportedly had to use their own credit cards to make purchases for Mr Pruitt and, according to The Washington Post, one staffer was never reimbursed for some of her expenses.

Water temperature: Simmering. Assigning government staffers to conduct personal business during work hours or to provide uncompensated help is a big ethical no-no. If any of the organisations approached for help with Ms Pruitt's job search had business before the EPA, that would be a particularly egregious violation.

Reassigned staffers

Mr Pruitt's first security head wasn't the only senior EPA officials moved to different duties once the new administrator arrived.

Per the New York Times, at least five officials - including one veteran of the Trump presidential campaign - were "reassigned or demoted" or otherwise moved after they questioned the agency's "spending and management" under Mr Pruitt.

It shouldn't come as much of a surprise that career EPA employees have been uncomfortable under the direction of a man who had railed against the agency - and filed lawsuits challenging its actions - prior to taking the helm.

Water temperature: Luke-warm. Personality clashes are inevitable, and it's difficult to determine whether these moves are because of legitimate policy differences or retribution for attempts to prevent wasteful spending and abuse of power.

Rewarded staffers

Two political appointees who followed Mr Pruitt to the EPA from Oklahoma were given sizeable pay boosts, apparently over the objection of the White House.

The EPA used a provision of a clean-drinking-water law to supplement the salaries of the aides - to the tune of $57,000 in one case and $28,000 in another - after the White House had rejected a direct request for a salary increase.

According to The Atlantic magazine, the move angered long-time EPA staffers, who viewed it as a misuse of money allocated by law for hiring scientific and engineering professionals

In a testy interview with Fox News, Mr Pruitt said he only recently learned of the pay boosts for his two close aides and have ordered that they be rescinded. The Washington Post, however, cites EPA officials on background saying the administrator authorised the moves himself.

Water temperature: Steaming. This one probably won't make much of a dent in public opinion, but the folks in the White House certainly won't be happy about Mr Pruitt flouting their directives.

His ambition

Mr Pruitt has reportedly been angling for a chance to rise above his current EPA station, potentially seeking to be the next US attorney general if Jeff Sessions, who has fallen into disfavour with the president, were to get the axe.

The rumours were growing thick enough that the president felt compelled to debunk them himself in a Friday morning tweet.

The former Oklahoma attorney general may also have an eye toward his home state, which could explain his frequent visits. There's a governor's election there this November, and the former attorney general would rocket to the front of the pack if he threw his hat in the ring.

Water temperature: Cool. Aspirations for higher office are hardly scandalous in Washington, although furtively lobbying for jobs that are currently filled - even when the current occupant is the oft-beleaguered Sessions - is a bit unseemly.

Why Pruitt resigned and what happens next?

On Thursday morning CNN quoted an unnamed senior White House official saying that the Pruitt controversies were "inching toward the tipping point". It turns out that point was very close indeed.

The EPA chief had managed to hold out longer than most expected as a cavalcade of controversies mounted, each alone enough to fell a Cabinet appointee in a past administration.

Mr Pruitt had survived due to a combination of the vigour with which he advanced the conservative goal of paring regulations and weakening the agency and Mr Trump's natural reluctance to cede to a political outcry.

In the end, however, it was Mr Pruitt who had been weakened beyond repair - hobbled by allegations of abuse of the power and privileges of office. Mr Trump had come to Washington pledging to "drain the swamp", and Democrats - with mid-term elections looming - were poised to point to Mr Pruitt as a prime example of how the swamp had consumed the president and Republicans in general.

With Andrew Wheeler - a former coal industry lobbyist - set to run the agency for the immediate future, little will probably change as far as policies and priorities within the EPA. Many Republicans in Washington, who were growing uneasy with Mr Pruitt's seemingly never-ending bad press, will surely be happy with the change.

Their relief, however, may be tinged with a certain amount of regret. Mr Pruitt had proven to be an effective champion of the conservative fight against the EPA - and even environmentalists had recognised him as a formidable adversary.

Mr Pruitt himself had aspirations for higher office - either within the administration or back home in Oklahoma. While political careers these days are rarely permanently ended, at least for the moment his has been seriously derailed.