The buck's latest surge comes as rising Treasury yields attract funds, and so-called 'U.S. exceptionalism' - a strong economy containing many of the world's biggest and most successful companies - encourages global investors to buy American assets.

The Dow Jones Industrial Average and S&P 500 erased most of the morning's losses at midday Wednesday, but small caps were down sharply. Nvidia tested a key level after suffering a huge drop on Tuesday.