The vast majority of Americans are under the impression that money laundering is something that is done by foreign dictators with shady banks in Latin America through anonymous shell companies. The Panama Papers revelation seems to bear that out.
However, the real home for money laundering in the world isn't some distant country, and it doesn't involve some complicated accounting. The favored target for money laundering is the real estate market of the United States.

After years of lambasting other countries for helping rich Americans hide their money offshore, the U.S. is emerging as a leading tax and secrecy haven for rich foreigners. By resisting new global disclosure standards, the U.S. is creating a hot new market, becoming the go-to place to stash foreign wealth. Everyone from London lawyers to Swiss trust companies is getting in on the act, helping the world’s rich move accounts from places like the Bahamas and the British Virgin Islands to Nevada, Wyoming, and South Dakota.
“How ironic—no, how perverse—that the USA, which has been so sanctimonious in its condemnation of Swiss banks, has become the banking secrecy jurisdiction du jour,” wrote Peter A. Cotorceanu, a lawyer at Anaford AG, a Zurich law firm, in a recent legal journal. “That ‘giant sucking sound’ you hear? It is the sound of money rushing to the USA.”
Rothschild, the centuries-old European financial institution, has opened a trust company in Reno, Nev., a few blocks from the Harrah’s and Eldorado casinos. It is now moving the fortunes of wealthy foreign clients out of offshore havens such as Bermuda, subject to the new international disclosure requirements, and into Rothschild-run trusts in Nevada, which are exempt.

The U.S. “is effectively the biggest tax haven in the world”
—Andrew Penney, Rothschild & Co.

That doesn't fit into the typical American's idea of the world, does it? Dirty money from Latin America is actually moving north to the United States for laundering, not the other way around.
However, this information leaks out to the general public when its convenient. For instance, when the target is Donald Trump.

The video was produced to help raise tens of millions of dollars through a controversial government program that offers expedited visas to foreign investors overwhelmingly from China. While the program has many supporters who argue it attracts foreign capital and creates jobs at no U.S. taxpayer cost, congressional overseers and Homeland Security have raised sharp concerns. Applicants are sometimes cleared in less than a month and the critics say the government is essentially selling visas to wealthy foreigners with no proven skills, paving the way for money laundering and compromising national security.

It's awful that Donald Trump is engaging is what is essentially semi-legal money laundering. Well, it's awful when Donald Trump does it.
When everyone else is also doing it, it doesn't seem that important.

Research conducted by the Homeland Security officials suggests that the majority of real estate purchases of at least $1 million in Florida's Miami-Dade and Broward counties are made through shell companies, said John Tobon, deputy special agent in charge at Homeland Security Investigations in Miami.
Money trails linked to drug trafficking, foreign corruption and other criminal activity often lead to luxury real estate properties, but when agents try to determine the true, or "beneficial" owners, they find only documents listing shell companies, many of which in turn are owned by other shell companies, Tobon said.

When it comes to ease of setting up anonymous shell companies, the United States ranks either second (after Kenya) or third.
Panama actually comes in 13th easiest, making their accounting standard and ethics much higher than the United States.

“No state in the US requires beneficial ownership information. So it’s practically everywhere,” explained Shah, who lives in Virginia. “Some states are easier than others. In some states it’s more money than others, because they also have tax-friendly laws. Delaware and Nevada and Wyoming are infamous – or famous, however you look at it – [for their tax laws]. Texas and Florida are equally easy.”

"In Delaware, for instance, you need to provide more information to obtain a library card than to start a company."
- Financial Transparency Coalition

You might remember that Enron used shell companies to hide their losses until it was too late.
So on one end you have anonymous shell companies with very low reporting standards. You can then use those shell companies to buy real estate, with equally low reporting standards.

At the moment, the law doesn’t require lawyers and real estate agents to know their clients and their credentials thoroughly.

This is not some hypothetical money laundering loophole we are talking about here. It's a big, big deal.

Meanwhile, there were about $104 billion in transactions involving foreign investors in the U.S. real estate market between April 2014 and March 2015. More than half the buyers in those deals were from China, Canada, India, Mexico, and the United Kingdom, and the majority of transactions involving overseas buyers were in cash, said Deborah Friedman, who works in the FBI's money laundering intelligence unit, in September.
Those purchases were concentrated in Florida, Texas, Arizona and California, she said.
The Patriot Act of 2001 required the Treasury to either issue rules on anti-money laundering controls and reporting of suspicious activity by real estate professionals or grant an exemption. The exemption has been in place now for more than a decade.

Of course eliminating this exemption might pop some very large real estate bubbles on the east and west coast.