public sector economics, he also authored other important macroeconomics papers. One of his more well-known papers in this field was his investigation with Charles Horioka of investment behavior in various countries. He and Horioka found that in the long run, capital tends to stay in its home country — that is to say, a nation's savings is used to fund its investment opportunities. This has since been known as the "Feldstein–Horioka puzzle." In 1997, writing about the upcoming European monetary union and the euro, Feldstein warned that the "adverse economic effects of a single currency on unemployment and inflation would outweigh any gains from facilitating trade and capital flows" and that, while "conceived of as a way of reducing the risk of another intra-European war", it was "more likely to have the opposite effect" and "lead to increased conflicts within Europe and between Europe and the United States." In 2005, Feldstein was widely considered a leading candidate to succeed chairman Alan Greenspan as Chairman of the Federal Reserve Board. This was in part due to his prominence in the Reagan administration and his position as an economic advisor for the Bush presidential campaign. The New York Times wrote an editorial advocating that Bush choose either Feldstein or Ben Bernanke due to their credentials, and the week of the nomination The Economist predicted that the two men had the greatest probability of selection out of the field of candidates. Ultimately, the position went to Bernanke, possibly because Feldstein was a board member of AIG, which announced the same year that it would restate five years of past financial reports by $2.7 billion. Subsequently, AIG suffered a serious financial collapse that played a central role in the worldwide economic crisis of 2007–2008 and the ensuing global recession. The firm was rescued only by multiple capital infusions by the U.S. Federal Reserve Bank, which extended a $182.5 billion line of credit. Although Feldstein was not explicitly linked to the accounting practices in question, he had served as a Director of AIG since 1988. In March 2007, the Lynde and Harry Bradley Foundation announced that one of four 2007 Bradley Prizes to honor outstanding achievement would be awarded to Feldstein. On September 10, 2007, Feldstein announced that he would be stepping down as president of NBER effective June 2008. Feldstein served as a member of the President's Foreign Intelligence Advisory Board from 2006 to