The book as a whole covers the world of global organized crime, in fact the whole title is "A Thieve's World: Threat of the New Global Network of Organized Crime". Wanta is specifically mentioned in a section of the book, titled "The Great Ruble Scam", extending from page 169 to 225.
While the book can be rather speculative and maddenly vague at times, the author, Claire Sterling, suggests that Leo Wanta actually did participate in the ruble trade, as Wanta himself insists. Although she did not have him connected to the the US government, as Wanta claims he was a Secret Service agent, but tied to a shadowy group of mafia figures.
Wanta apparently did try to buy rubles at discount rates, at one point 140 billion rubles, but the deal fell through, ironically because of the US government. From page 180:
Whether or not Yeltsin consented personally, his closest adviser, Gennady Burbulis, did so implicityly: the proposal was referred to him, and he did not object. In fact, the Comission of Inquiry found an agreement already drawn up by Silaev's cabinet, accepting Wanta's offer. The agreement fell through, or seemed to, when the U.S. State Department warned that Wanta "had major debts and some credit card problems." ("I confronted him in November 1990, and he fled," said the chief investigator, Kalinichenko.)
It is also interesting the earliest mention of Wanta's involvement was in October 1990, because Wanta himself insists that then President Reagan sent him on this mission. Reagan of course left office in January of 1989.
There were evidently several attempts by various organized crime figures to buy up Russian rubles on the cheap, either as part of their crime business, such as money laundering, or an attempt to then get Russian resources, such as oil or gold at a discount. Most of these attempts failed, but some apparently succeeded, thus the title "The Great Ruble Scam". The author found no evidence that Wanta ever accomplished this though, and certainly not on the scale he has boasted about, in the hundreds of billions, or even trillions of dollars. In fact the entire value of Russian Rubles in 1990 was cited as $10 billion, hardly enough to for one person to make trillions of off trading.
The one trade which Wanta apparently was successful at was getting, was a contract to export petroleum, and import food, although no amount of money is cited. Sterling also speculates that Wanta may have been connected to a considerable amount of missing Russian gold, 2000 tons, although the only proof she gives for that is Wanta claiming that he was trying to sell large amounts of gold. It is odd that she just believes him, considering she spends the rest of the section, saying what a con man he is. From page 186:
Leo Emil Wanta, born in Appleton, Wisconsin, was a fifty-year-old, heavyset snake oil salesman, as Mr. X described him. Starting in out in the pinball machine business in Menomonee Falls, he had gone on to "work credit card and many, many other scam," said a senior FBI official.
For the U.S. Secret Service, where the files on him are a yard long, he is a "flim-flam artist," convicted in Switzerland for money laundering involving the Charleston Bank in Panama, deported to the United States to stand trial for tax evasion and wanted in Austria for aggravated fraud arising out of events going back to September 1990, just as he was moving in on the Russian government.
An eclectic trader, Wanta faxed offers to a worldwide clientele in the summer of 1990, including atropine tablets from Germany; ten million jute sandbags from Saudi Arabia; twenty million cartons a month of tax-free Marlboros from the Ukranian capital of Kiev; and two million gas masks from the U.S.S.R. "while the supply lasts." Apart from miscellaneous goods, Wanta was trading not just in rubles but in lire, yen, pesetas, deutche markes, Swiss francs, pounds sterling, and Singapore dollars for commissions up to 14 percent - the clear mark of a money launderer.
All in all, it appears he was up to something, but the line between fantasy and reality, becomes quite blurred.