Why did the United States fail to ratify the Kyoto Protocol?

Short Answer : The Kyoto Protocol was signed by President Clinton, but Senate refused to pass it. President Bush rejected the Kyoto Protocol, and the Kyoto Protocol was consequentially killed.

Long Answer:

A resolution was passed in Senate on the qualifications for which a treaty would have to meet for Senate to pass it. The Kyoto Protocol did not meet these standards; not only did the Senate as a whole not one to pass it, it wasn't allowed to pass it. The main concerns were that firstly, many developed countries were not participating in it, and secondly, there were fears that the Kyoto Protocol would harm the American economy (especially the coal industry) and either way wouldn't be very effectual at combatting global warming.