From the great David Goldman:
When Reagan took office in 1981, the baby boomers were in their 20s and 30s, America had a 10% savings rate, the current account was in surplus, and America was the world’s largest net creditor nation. Reagan was able to cut taxes and finance an enormous budget deficit because the world’s demand for US Treasury securities was correspondingly large. In 2010, the baby boomers are in their 50s and 60s, America has saved nothing for a decade, the current account remains in severe deficit and the world is choking on the existing supply of Treasury securities. Cutting taxes to stimulate the economy is not as simple this time round.