As a form of Checks and Balance, president wasn't granted with the power to make laws. The president only has the power to give a proposal/suggestion. These suggestion need to be approved by the congress before it can be passed. So eventually, The power to make laws were controlled the legislative branch of the government.
In order to control the power of the legislative branch, the president is given with the power as the 'chief legislator'. This position allow the president to give veto toward the laws that are passed by the legislative branch.
