In reality many other forces are driving the dollar down, including a perception that it is relatively stable compared to other currencies and what appears to be a recovering trend in the US economy. Many investors are moving away from dollars to more volatile investments because the dollar is not offering the high returns which come from riskier investments.
The weakness of the dollar is also beneficial to other sectors of the US economy. As was demonstrated during the Bush administration, keeping the dollar weak can create liquidity for the government by attracting investors in government debt. Similarly, a weak dollar stimulates the economy and the stock market by attracting foreign investors to the United States looking for bargains. Stimulating economic growth and maintaining government solvency are a lot more important to the Obama administration in its desperate quest for economic recovery than Iran's largely symbolic decision to trade in euros rather than dollars.
The real danger in the economy and for the government is not what currency Iran is trading in, but the high level of unemployment, which reached a 26 year high of 9.8% this week. More unemployment means smaller payrolls, which means less tax revenue for a government that is desperately overextended in debt. Raising taxes will just lead to more problems for business, more layoff and ultimately even less government revenue. This also drags the value of the dollar down, because despite the claims of some theorists on the fringe, whatever real value the dollar has derives from GDP — not oil — and lower employment and fewer operating businesses means a lower GDP.
The solution to the decline of the dollar is not to invade Iran, but to address the problems with the domestic economy. Just attracting more foreign investment with a weak dollar is insufficient for real recovery because it does not create a significant growth in employment or the domestic economy. The key to real economic recovery is ending the flight of businesses and their operations to other countries. This can only be done by making it more profitable to do business in America than to do it elsewhere. This can most easily be accomplished by reducing overhead. The obvious way for the government to achieve that is by lowering corporate taxes.