Absent such proof, though, even such “shady” behavior may be permissible, she said. “Campaigns do have a fair amount of leeway to determine how much space they need and how much to spend for it.”

Erin Chlopak, once an FEC attorney and now with the Campaign Legal Center advocacy group, said Trump’s use of campaign money for his personal benefit might be illegal ― if it can be proven that the Trump Tower office is not serving any legitimate campaign purpose.

“The reality is there would be even more commercial space available in Trump Tower,” the former staffer said, also on condition of anonymity. “Glassner goes there daily so they can rationalize it.”

One former campaign staffer says that value is obvious: at least in terms of Trump’s personal bank account. The building has been shedding commercial tenants since he became president, and currently has 41,271 square feet available for rent across five floors. Should Trump move the remaining New York staff into the Arlington office, it would leave yet more vacant office space in a building whose rents continue to put money into his own pocket.

The informal adviser, who spoke on condition of anonymity, said that while most of the staff have been transferred to Arlington, Trump and top campaign officials want to keep the Trump Tower presence. “They think it’s a valuable asset to have,” the adviser said.

The precise cost per square foot for the Trump Tower office, though, cannot be determined using Federal Election Commission records and publicly available real estate documents. The Trump campaign denied a HuffPost request to visit that office and refused to disclose its size.

No more than “four or five” campaign staffers work at Trump’s Manhattan base, according to an informal adviser close to the White House, where the campaign rents a few thousand square feet as its “headquarters.” The per-square-foot cost is likely at least triple what the Republican National Committee pays for the much larger space it shares with the campaign in Arlington, according to a HuffPost analysis.

NEW YORK — With commercial tenants fleeing his Trump Tower, President Donald Trump continues to spend $37,500 a month of campaign money for office space there — with some of that cash destined for his own wallet ― even as thousands of square feet go unused at a newly opened office in northern Virginia.

Robert Weissman, president of the liberal government watchdog group Public Citizen, said Trump’s decision to funnel campaign money to himself is striking, given how the campaign brags about its small contributions from middle-income and elderly supporters.

“It’s an especially consequential betrayal to waste campaign money when so much of it comes from small donors for whom the donations are a real financial expense,” he said. “To have a purported billionaire taking money from people who are contributing in $10 and $20 increments to bulk up his own his bank account is pretty pathetic. But I guess not surprising.”

A Self-Dealing Campaign

While Trump describes himself as a billionaire many times over, his personal enrichment by Republican political groups, foreign governments and U.S. government agencies that use his hotels and resorts has been a defining feature of his presidency.

As a candidate, he pledged that he would separate himself from his family business were he elected. He reneged on that promise almost immediately, retaining both a direct financial interest in the various enterprises as well as control through his adult sons.

When he announced his campaign in June 2015, Trump based it in on the fifth floor of his 57-story building a few blocks from Central Park. At the time, he was largely self-funding his campaign, and the rent he charged himself was $35,458 a month for 13,100 square feet of space that had been used as a set for his reality TV game show, “The Apprentice.”

A year later, after Trump had secured the nomination and GOP donors began paying for his campaign, he started charging it nearly five times that much, $169,758 per month, although the campaign also began using the floor directly above the fifth floor, the 14th.

(Trump Tower’s floor numbering scheme was designed to make it seem taller than it is. Floors six through 13 do not exist. Nor do 27, 28 or 29.)

After winning the presidency, Trump took the unprecedented step of opening his reelection campaign the day he was inaugurated. Former presidents George W. Bush and Barack Obama, in contrast, did not open reelection accounts until their third years in office.

That immediate start to his reelection allowed Trump to start collecting and spending donor money right from his first days in office. And among Trump’s expenses have been payments to his own for-profit businesses — the largest of which was rent to his commercial and residential tower in midtown Manhattan.

During 2017 and 2018, Trump spent $890,163 in campaign money donated for his reelection toward Trump Tower rent, another $53,900 in rent for a nearby apartment that he owns, and $42,225 for an apartment on Central Park South.

The White House informal adviser, who is also a prominent Republican donor, said campaign staff and consultants visiting the city for fundraisers and other events use the apartments, thereby reducing the need for hotel expenses.

It is unclear, though, if the $96,125 in rent for the two apartments each year is less than what occasional visitors to the city on campaign business would have spent at hotels. Also unclear is the campaign purpose for $52,000 in “rent” payments to “Trump Restaurants LLC,” the entity that operates his branded eateries in Trump Tower.

‘Trump Tower is ruined.’

Yet the biggest unanswered question may be why Trump needs a New York campaign headquarters at all.

The campaign has been describing with some pride its ability to acquire a fully furnished upper floor in a 19-story building in Arlington’s Rosslyn neighborhood by purchasing a sublease at a low price. The expansive windows offer sweeping views across the Potomac River and onto Washington, D.C.’s monuments and tidal basin.

Two hundred miles north, on New York’s Fifth Avenue, the occupancy rate at Trump Tower has fallen from 99 percent to 83 percent in recent years, according to a recent Bloomberg analysis. The building’s vacancy rate is now twice the average in Manhattan. Nike, as one example, which occupied 65,000 square feet for a massive store, left in 2018.

Before Trump’s campaign, Trump Tower had been able to charge considerably more per square foot than was available at nearby buildings in the pricey “Plaza District.” Now, the opposite is true, and Trump Tower is listing prices as “negotiable,” Bloomberg reported.

“Who would want to operate a space there, with all that security?” the former campaign staffer said.

“Trump Tower is ruined,” the White House adviser said. “Maybe because he’s a Republican guy in New York. Maybe all the security ... I wouldn’t live there. It’s like a war zone.”

The Trump campaign did not respond to numerous HuffPost queries for this article, including a request to determine the size and configuration of its Trump Tower campaign office.

A total of 14,888 square feet of useable space are on that floor, which is labeled the 15th, but which is in reality only the seventh story.

Of that, 4,972 is currently empty and on the market with an asking price of $85 per square foot per year. An office for a clothing designer is also on that floor, as are some offices for the Trump Organization, Trump’s closely held family business.

One real estate broker familiar with the campaign office, speaking on condition of anonymity, described it as “small.”

Trump is spending $37,542 of campaign money per month for the Trump Tower space — $450,500 a year. If the campaign occupies 5,000 of the 9,916 feet not on the market on that floor, that would work out to $90 per square foot annually.

In contrast, for 21,257 square feet in Arlington, Trump’s RNC paid $667,639 a year ― $31 per square foot. Journalists who have been invited for tours recently have reported that most of the desks sit unoccupied — waiting for the election season when hiring is set to ramp up for both the RNC and the Trump campaign.

Jordan Libowitz, with Citizens for Responsibility and Ethics in Washington, said Trump’s campaign has been sending money to Trump the private individual from the start of his presidential run. “It is far from transparent and appears to be putting a lot of money from campaign donors right into the president’s pocket,” Libowitz said. “While it is allowable as long as the campaign is paying market rate, it is very hard to know if everything is on the up and up from public disclosures alone.”