The Constitution gives Congress the most power of any of the branches of the US government. The US government was originally meant to be dominated by Congress, not by the president.
Congress has a great deal of power to create economic policy. Congress has the power to raise and lower taxes. Congress has the power to do things like passing economic stimulus bills. It has the power to create and to do away with regulations that govern what businesses are allowed to do. Congress has the power to borrow money. All of these powers are granted to Congress (either explicitly or implicitly) in Article I, Section 8 of the Constitution.
Though Congress has almost all the power, we tend to hold it less responsible than the president because it is a huge body made up of many people. In Congress, there is no one person upon whom to lay the blame when things go wrong.