Towards the end of the presidential election in 2016, it was discovered that both candidates, Donald Trump and Hillary Clinton, shared one notable similarity: an office in Wilmington, Delaware that had become famous for helping thousands of companies avoid hundreds of millions of dollars in taxes through the so-called “Delaware loophole.”

The nondescript, two-story building at 1209 North Orange Street in Wilmington is home to over 285,000 companies including Apple, American Airlines, Walmart and the two former presidential candidates.

Officially named Corporation Trust Centre (CTC), it was investigated by The Guardian in August of 2016, three months before the election.

Unbeknownst to the general public, being registered in Delaware allows companies to take advantage of strict corporate secrecy rules, business-friendly courts and the “Delaware loophole,” which can allow companies to legally shift earnings from other states to Delaware, where they are not taxed on non-physical incomes generated outside of the state.

The Delaware loophole is said to have cost other states more than $9 billion in lost taxes over the past decade and is considered one of the world’s most popular locations for tax evasion.

Another example includes Ugland House, a five-story building in the Cayman Islands that Barack Obama called “either the biggest building in the world, or the biggest tax scam on record.” It served 18,000 registered companies.

Neither candidate from the 2016 election has explained why they registered at the Delaware office.

Reportedly, Hillary Clinton collected more than $16 million in public speaking fees and book royalties in 2014 through CTC, according to the Clintons’ tax return.

After stepping down as secretary of state in February 2013, Clinton quickly registered at CTC. Incidentally, her husband Bill set up WJC LLC, a vehicle to collect his consultation fees, at the same address in 2008.

A spokesman for Hillary Clinton said: “ZFS was set up when Secretary Clinton left the State Department as an entity to manage her book and speaking income. No federal, state or local taxes were saved by the Clintons as a result of this structure.”

As for Trump, out of 515 companies on his official Federal Election Commission (FEC) filing, 378 were registered at CTC.

Some of Trump’s investments there included Trump International Management Corp and several companies that formed part of Hudson Waterfront Associates, which aimed to build luxury condominiums in Manhattan.

Accounting experts say there are many legitimate reasons why U.S. and foreign companies incorporate in Delaware, particularly because of its highly respected Court of Chancery and business-friendly state government.

Additionally, setting up a company in the state is incredibly easy: it takes only a few hours and requires less paperwork than registering for a library card in Delaware. Subsequently, there are more than 1 million companies registered in the state – which has a population of only 935,000.

This development in the lead-up to the 2016 election was notable for various reasons, the least of which that it countered the very campaigns of both nominees. Clinton called offshore tax havens, which would include Delaware, “a perversion” of the legal code. Some analysts viewed her claim as an attempt to distance herself from accusations of being too corporate by then-Democratic rival Bernie Sanders. Trump had also said he supported raising taxes on the wealthiest Americans, “including myself,” through his tax plan offers cuts.

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