Why did the framers want the president to be weaker than congress?

Read: 

Article. I. - The Legislative Branch 
Section 8 - Powers of Congress 

Article. II. - The Executive Branch 
Section 1 - The President 
The Constitution was set up in such a way that no one branch of government would have absolute power. The Legislative branch (Congress) has the ability to make laws, the Executive branch (The President) has the power to veto laws made by Congress. Another built in check to presidential power is Congress' ability to override a veto with a 2/3 majority vote. This means that the will of the people (by way of their elected representatives) has more weight than that of any one person. The Judicial branch has the power to declare any law unconstitutional, but justices are appointed by the president and confirmed by congress to ensure impartiallity. 
In theory, the Legislative branch has the most tangible power, but often in practice single leaders have more political power.
It would appear to me that the Founders meant for the president to be weaker than Congress... and it would appear that "I am the decider" George W. Bush has way overstepped his authority.