Actually, the US Government has done just that when FDR seized, not 40% but 100% of the money, money in the form of perfectly legitimate gold coins in the 1930's. Astoundingly, a descendent of bankers, and son of a robber baron, had become convinced gold coinage was the root of economic evil, following WWI and the Roaring 20's where the US had amassed a large amount of the world's gold inventories, a disproportionate share even. WIth it's peak, FDR for some reason didn't want gold flows diluting his political power to fundamentally change capitalism to quasi-socialism. Gold would have quickly told the tale of the tape regarding the New Deal, and an honest economic poll is the last thing FDR wanted. He, like O', seems to prefer talking.