I disagree with post #1. Beginning with President Washington every Presidential Administration (Executive Branch) has had a 'policy agenda'. Constitutional Framers Alexander Hamilton, James Madison, and John Jay understood that the executive policies of the president weild power and that power must be kept in check. Several essays in The Federalist Papers discuss how the policies of the Executive Branch can be 'checked' and analyzed by the Legislative and Judicial Branches of government. I've listed two examples from U.S. history that show how the Executive branch is subject to review from the other branches of government.
1. President Wilson promoted his foreign policy agenda for a League of Nations, the Legislative Branch rejected it.
2. F.D.R. tried to push his policy to have the Legislative Branch alter the composition of the Supreme Court so that some of his New Deal policies would not be overturned by the court. The Legislative Branch defeated his proposal.
3. Currently, the president's healthcare policy which was passed by the Legislative Branch is being argued in the Supreme Court regarding its constitutionality.
The legislative branch is the law-making entity. The executive branch usually sets the agenda, which policies they are pursuing and which they don't like, etc. Legislators usually respond to the executive branch, especially in terms of political party. For example, a Democratic executive branch might focus on one policy, and a Republican congress might be interested in undermining it.
The judiciary largely has no role in this. The bulk of this is done by the executive branch since the governmental agencies that carry out policy belong to that branch. The legislature might do a little of this through the staff of the appropriate Congressional committees, but it is largely an executive branch function.