e each department of the government monitors itself, it is also monitored by the other branches of government. We see the basic thinking behind this in The Federalist Papers, No. 51:
In a single republic, all the power surrendered by the people is submitted to the administration of a single government, and the usurpations are guarded against by a division of the government into distinct and separate departments. In the compound republic of America, the power surrendered by the people is first divided between two distinct governments, and then the portion allotted to each subdivided among distinct and separate departments. Hence a double security arises to the rights of the people. The different governments will control each other, at the same time that each will be controlled
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