In politics of the United States, "fourth branch of government" is an unofficial term referring to groups or institutions perceived variously as influencing or acting in the stead of the three branches of the US federal government defined in the Constitution of the United States (legislative, executive and judicial). Views as to whether the influence is due or undue or the actions are for good or ill also vary.
Such groups can include the press (akin to the European 'Fourth Estate'), the people (in sum or as grand juries), and interest groups. The independent administrative agencies of the United States government, while technically part of any one of the three branches, may also be referred to as a 'fourth branch'.
The press
While the term 'fourth estate' is used to emphasize the independence of 'the press', the fourth branch suggests that the press is not independent of the government. The concept of the news media or press as a fourth branch stems from a belief that the media's responsibility to inform the populace is essential to the healthy functioning of democracy.
Douglass Cater, in his 1959 The Fourth Branch of Government offered the hypothesis that the press had become "a de facto, quasiofficial fourth branch of government" and observed it was the looseness of the American political framework that allowed news media to “insert themselves as another branch of the government”. Cater was "convinced that, insofar as the press did act as a true political player (rather than an unbiased observer of politics), it corrupted itself and went astray from its primary responsibility—to convey important information and to act as a nonpartisan watchdog for the public against all trespassers on their rights."