In April 2018, President Trump’s Mar-a-Lago Club charged taxpayers $3 so that Trump could drink water.

That charge was one of many bills that Mar-a-Lago sent to the State Department after Trump used his own club to host a summit with then-Japanese Prime Minister Shinzo Abe. We reported it on Tuesday, in an article that revealed Trump’s company has received at least $2.5 million in government payments since the president took office.

I wrote that article, after months of reporting on the subject with a team of colleagues. How did we figure it out?

We started by asking the State Department.

The first time was eight months ago.

“I request copies of any documents from the State Department’s Regional Financial Management System - Disbursing Voucher Information Details forms where the vendor name is any of the following,” we wrote on Feb. 21 in a Freedom of Information Act request. What followed was a long list of Trump properties, including Mar-a-Lago.

That didn't work.

By law, the State Department was supposed to make a determination within 20 business days. But for years, it often hasn't met that deadline. The average response time for “complex” requests like ours is 307 days, according to State Department statistics.

In our case, 20 days passed. We got nothing.

So, six months ago, we tried asking the State Department’s press office. They had released some records of payments to Trump properties but few after October 2017. We wanted the rest, including records from Abe’s visit in 2018.

“Can you provide details of State Department payments to Mar-a-Lago or any Trump-branded property” since October 2017? I wrote in an email on April 22.

That also did not work.

“Would you be willing to accept responses off the record?” a State Department spokesperson wrote back.

We said no. Information provided “off the record” typically means that it can’t be included in the article in any form. That’s not much help to readers. The State Department declined to say anymore.

So, four months ago, we sued the State Department.

“The Post requests a declaratory judgment that the State Department has violated FOIA and that the Post is entitled to immediately receive the documents referenced above,” said our lawsuit, filed in June in federal court in Washington.

That seemed to work.

At first.

“State has collected approximately 450 pages of potentially responsive documents,” the government said in a court filing in August. In that filing, the department said it would “aspire to process potentially responsive records at a rate of 300 pages” and release the first batch on Oct. 15.

We had hoped the State Department would follow the example of the Secret Service, which we had also sued. The Secret Service released hundreds of pages of records showing payments to Trump properties.

But the State Department did not do that. When Oct. 15 came, it released just two pages.

Instead of revealing the full history of the State Department’s taxpayer-funded payments to the sitting president’s businesses, the records showed a single $8,300 payment to Trump’s golf club in Ireland. The president’s daughter-in-law had visited the club in 2019. The club had charged the Secret Service for agents to follow her — following a common pattern, in which travel by Trump’s children and their families forced the government to spend money at Trump properties.

The rest of the pages likely wouldn’t be released until mid-November at the earliest, the State Department said. That meant we wouldn’t see them until after the 2020 election.

They said that was because so many different government agencies had been involved in the payments. Now, the State Department needed them to sign off on releasing the records.

The very fact that made these payments interesting — that they showed that multiple parts of Trump’s government had all spent money at Trump’s properties — was now a reason to delay their release.

“All of the responsive records in this case require external consultation with Executive Branch components, and some require multiple such consultations,” the government said in a legal filing last week.

Journalists often speak of trying “the front door,” which means asking for information through established channels: the press office and the public-records process. At other agencies, that had worked: The Defense Department responded to our public-records request without a lawsuit, providing records of more than 3,000 transactions at Trump properties.

But, at the State Department, we had tried all the front doors. We’d gotten all of two pages.

The question we started with — how much had the State Department spent at Trump’s properties? — was as much a mystery as it was in February.

So, two weeks ago, we tried something new. We didn't ask the State Department.

We asked everybody else.

That worked.

Within a few days, we had obtained documents that showed payments the State Department had never previously disclosed. We reviewed those documents, compared them with documents we had already obtained from other sources and concluded they were authentic. They showed catering bills from Mar-a-Lago during Trump’s summits with Abe and Chinese President Xi Jinping. Included in those bills was a $6,000 charge to taxpayers for floral arrangements during Abe’s 2018 visit.

And the $3 bill for Trump's water.

That was a powerful illustration that Trump has set up a hidden business relationship with his own government, which lets him effectively buy services from himself.

In this case, Trump's club sold the water. Trump drank the water. Then Trump’s club billed the taxpayers.

But, although that purchase happened 2½ years ago, taxpayers didn’t know until Tuesday.

The Washington Post asked the State Department for comment on this article on Thursday.

It has not responded.