The three branches of government are supposed to interact with one another through checks and balances. The three branches each have their own distinct powers through the idea of separation of powers. However, they also share in one another’s powers so that it will be possible for them to check and balance one another.
In a sense, the three branches are not supposed to really interact. Each is supposed to have its own set of powers. The legislature is supposed to make the laws while the executive branch enforces the laws and the judicial branch interprets the laws. If this were how things worked in reality, there would be little interaction between the two branches.
However, the Framers of the Constitution also inserted checks and balances into the Constitution. They did not want any branch of government to be able to gain too much power. Therefore, they gave each branch ways to interfere in the others’ powers. This means that the various branches need to interact to some degree. This is particularly true of the legislative and executive branches.
The legislative and executive branches are supposed to work together to some degree. Because the president has the power to suggest laws and to veto laws he does not like (as well as to do things like proposing budgets), the executive plays a role in making laws. The president and Congress are supposed to work together to make laws. Because the Congress has the power of the purse and the power of oversight over the executive branch, it has a role in determining how the laws are to be carried out. This means that the president and Congress are supposed to work together to execute the laws.
However, this does not mean that the legislative and executive are always supposed to be in accord with one another. The Framers built in the possibility of dissension between the two branches because they wanted it to be hard to make major changes in the law. They did not want a system of government in which one person or group could easily get their agenda passed. Because of this, the legislative and executive are supposed to have an ambiguous relationship, one in which they sometimes work together and sometimes work against one another.
The judicial branch is largely exempt from the explicit give and take that the other two branches engage in. The judicial branch can overturn decisions of the other branches, but it is not consulted in the decision-making process and does not really interact with the other branches. This is true because the judicial branch needs to maintain its non-partisan, unbiased image.
Because the Framers worried about excessive government power, they set up a system where the legislative and executive branches are supposed to work together to some degree, but are also supposed to be in opposition to one another at times.
Through the system of checks and balances, the three branches of government check on one another to make sure that no single branch has more power than the other. The executive branch can veto bills that the legislative branch creates. However, the legislative branch can override the veto with 2/3 of majority vote. They can also have the power to impeach the president. The executive branch also has the power to pardon the judicial branch and can appoint judges. The judicial branch can declare presidential acts unconstitutional, and can even declare bills (laws) that the executive branch creates unconstitutional. The power that the legislative branch has over the judicial branch is that they can approve federal judges.