What does the power of impeachment serve as a check on the president

The power of impeachment ensures that the president of the United States is not above the law. The president is a very powerful person, but he or she is not a monarch or tyrant. For the system to operate properly, he or she must obey the laws of the land.
Impeachment is part of a system of checks and balances that keeps one branch of the government from becoming too powerful and, therefore, having the temptation to abuse its power. For example, the judiciary branch has the power to declare any law the legislators pass unconstitutional. The legislature can refuse to pass legislation that the executive branch (headed by the president) wants to make law. In turn, the president can veto legislation Congress passes—and Congress can override the veto. All these mechanisms keep power dispersed: everyone knows there are limits to what they can do. They all know they have to—or are supposed to—work together.
Impeachment is yet another limit. If a president breaks the laws he or she has sworn to uphold, Congress has the right—and responsibility—to censure him or her, and, if necessary, remove him or her from office.