“In considering the desirability of political parties, it should be borne in mind that to a very real extent political parties militate against the principle of separation of powers by undermining the system of checks and balances. They do this by weakening the motivation of government official’s to resist encroachment.
Under the party system a government official’s ambition is best served by maintaining his standing with other members of his party. Hence, when persons influential in his party are involved in encroaching upon the authority of his department, his personal interest in remaining in their good graces is stronger than his personal interest in resisting their encroachment.
In fact, if he resists them at all, it is likely to involve a sacrifice of his personal interests rather than a furtherance of them. In other words, unity in support of party is likely to supersede unity in support of the Constitution.
“In considering political parties in the context of separation of powers and checks and balances, due concern should be given the possibility that all branches of the government maybe controlled by a single party. The danger to our freedom system inherent in that possibility was indicated by James Madison in the following words: ‘The accumulation of all powers, legislative, executive, and judiciary, in the same hands, whether of one, a few, or many, and whether hereditary, self-appointed, or elective, may justly be pronounced the very definition of tyranny.’”
(Jerome Horowitz, The Elders of Israel and the Constitution, p. 41. 1970.)