On 25 July, the conservative Heartland Institute is slated to host a one-day meeting at the Trump International Hotel, just a few blocks from the White House. It will feature leading climate science deniers who will discuss issues like “the benefits of ending the Democrats’ war on fossil fuels”, according to the institute.

Last month, as Donald Trump was kicking off his 2020 campaign and boasting again of “draining the swamp” of Washington’s powerful lobbyists and elites, a couple of dozen oil and gas executives with the Domestic Energy Producers Alliance were checking into the president’s hotel before a day of schmoozing with Republican House leaders and cabinet officials.

Welcome to the Trump hotel’s lucrative influence-peddling swamp in the heart of Washington DC.

Fossil fuel interests, pro-gun industry groups, conservative bigwigs, members of Congress, Trump’s 2020 campaign, foreign delegations and all manner of Trump allies flock to his landmark Washington DC hotel to cozy up to the administration, say watchdog groups, former Republican members of Congress and policy analysts.

Influence peddling by lobbyists, Republican donors and foreign government representatives who have frequented the Trump hotel for meetings and overnight stays helped to generate about $81m in hotel revenues for Trump through 2018, according to his financial disclosure forms.

The symbiotic ties between Trump’s hotel – which the president benefits from financially while his two eldest sons manage his real estate empire – and Washington’s lobbying and conservative worlds, have become commonplace in the Trump era. They have prompted lawsuits alleging foreign payments to the hotel violate an anti corruption clause in the constitution and prompted critics to say Trump is literally profiting from his presidency.

“Energy producers maximize their chances of getting every last thing they want out of the administration by spending as much as they can at the Trump hotel,” said Jerry Taylor, the head of the Niskanen Center, a nonpartisan DC thinktank that has rebutted climate skeptics and backs alternative fuels. “This is a transactional administration that pays attention to such things.”

Taylor called the Trump administration “easily the most corrupt and swampiest, if you will” in American history.

The Trump family attends the grand opening ceremony of the Trump International Hotel in Washington DC, on 26 October 2016. Photograph: Evan Vucci/AP

Likewise, the former Republican congressman Mickey Edwards said that the hotel poses a serious problem because “it provides another under-the-radar avenue for lobbyists to influence legislation and regulations”. Edwards stressed that “you have to be stupid to believe that Trump and his family don’t get reports about who is using the hotel”.

Robert Maguire, the research director of Crew, a nonpartisan government ethics watchdog, agreed. “President Trump and officials in his administration are feeding the ethical morass, frequenting his hotel and other properties and using their position to promote his businesses,” Maguire said.

Little wonder that the hotel has become a gravy train for Trump and his family, undercutting his pledges to drain the lobbying and big money swamp, say analysts.

Last year, Trump’s revenues from the hotel were just shy of $41m, a little less than 10% of his 2018 overall revenues of at least $434m, according to his financial disclosure forms. By contrast in 2017, Trump’s overall revenues were at least $452m, of which his hotel provided about $40m.

It provides another under-the-radar avenue for lobbyists to influence legislation and regulations Mickey Edwards

Even Trump’s daughter Ivanka notched $4m in revenue from the hotel last year, her 2018 financial disclosures reveal.

According to data compiled by Crew, as of late June Trump had visited the hotel at least 21 times, and executive branch officials have been there at least 263 times. Further, members of Congress or their chiefs of staff have been to the hotel at least 453 times, according to Crew.

Trump and his congressional allies have also capitalized on the hotel to do major campaign fundraisers. His campaign and the RNC hosted a fundraiser in 2017 at the hotel that pulled in just under $10m, according to reports. Last month, days after announcing his 2020 campaign, Trump held another money bash at the hotel that raised $6m for his campaign.

The hotel has become a money machine for key Trump congressional allies like the congressmen Jim Jordan and Mark Meadows who, respectively, held fundraisers there last month and in 2017.

Other conservative and business allies including the gun industry are also ponying up for hotel events, in some cases not long after Trump unveiled gun policies that could benefit them.

In late July firearms industry group the National Shooting Sports Foundation (NSSF) and another gun industry body, both of which have backed looser gun sales regulations, are slated to hold a three-day confab at the Trump hotel. The gun gathering comes after Trump announced this spring that he was abandoning a UN arms trade treaty, a move the NSSF praised.

On top of ethics issues, the hotel’s hefty business dealings with foreign governments have sparked lawsuits from congressional Democrats and two attorneys general alleging violations of an anti-corruption statute in the constitution.

Since Trump was elected, the hotel has become a favorite meeting and overnight spot for representatives from countries such as Saudi Arabia, Turkey, Malaysia and Nigeria, many of which have been tarnished by scandals and have been trying to burnish their images with the administration.

Moreover, an Iraqi sheikh this year spent a whopping 26 nights at the Trump hotel not long after advocating for a tougher US policy towards Iran, according to the Washington Post.

In separate lawsuits, about 200 congressional Democrats and attorneys general from Maryland and DC have charged that the foreign revenues received by Trump’s hotel violate the foreign emoluments clause, which bars any payments or gifts to the president and other federal officials without congressional authorization.

The justice department has gone to court to block the emoluments suits, arguing for a narrow and controversial interpretation of the law and echoing arguments made by Trump’s personal lawyers that only direct payments to Trump himself by foreign governments would be covered by the clause.

The congressional lawsuit made some headway in late June, when a federal judge in DC ruled that the suit could proceed with discovery. But last week, the justice department appealed the ruling, arguing again that only foreign payments made to Trump directly were intended to be covered by the emoluments clause.

This month, too, the emoluments lawsuit by the Maryland and DC attorneys general suffered a setback when a three-judge panel ruled they lacked standing to sue and called for the suit’s dismissal.

When he took office, Trump promised that profits from foreign business earned by the hotel and other Trump properties would be donated to the treasury, and so far checks totaling $343,000 have been written to cover 2017 and 2018. Still, critics say that it’s impossible to tell if these checks fully cover foreign payments to Trump properties in part because Trump – unlike other presidents – has refused to release his tax returns.

To Maguire, the welter of ethical and legal issues facing Trump’s hotel suggest it is “becoming harder and harder to figure out where the Trump administration ends and the Trump Organization begins”.