Who has the most power in the United States?

Think about the question before you answer. I'll give a few examples of power and you tell me which is more powerful.

There are three branches of the Government, The Legislative, The Executive and The Judicial. Which one is more powerful?

The Legislative creates the laws and passes them. The Executive Branch has to agree with the laws and sign them into being. The Judicial Branch interprets the law(s) when and if any questions are raised about the constitutionality of the law.

So, I ask you, which is more powerful? The House and the Senate Pass law A. The president shoots down law A and sends it back. The House and the Senate over-ride the veto and the Law goes into affect. The Judicial System looks at the law and says it's constitutional and it remains. Or inversely the Judicial System says it is not constitutional and it is killed there.

So, who has the most power here? The presidency is considered the most powerful office in the U.S. Government. However, The President is not a king, he can not get anything he wants for free, someone has to pay for him. He can demand all he wants from The Legislative Branch, but they can ignore him and do the opposite, but he still has to approve or deny, and even then they can over ride him.

So this brings my second question. How can President Obama demand the House and Senate leaders come to him like school children to the principal?