Question

how is power check and balanced in the national government?

Answer 1

Between the three branches of government - executive, legislative, and judical

Answer 2

To expand on cpm's answer, the three branches of the government, the Executive (President and his Cabinet), the Legislative (Congress and Senate), and the Judicial (Supreme Court) all check themselves, each has a specific power over the other, you can think of it like Rock Paper Scissors if that makes it easier for you. The powers are separated to ensure that the government of the United States isn't easily taken over by tyrants.