Prophets of Deceit (A Study of the Techniques of the American Agitator) is a 1949 book co-written by the German sociologist Leo Löwenthal and the Polish-Jewish scholar Norbert Guterman.

The authors analyze and define media appeals specific to American pro-fascist and anti-Semite agitators of the 1940s, such as the application of psychosocial manipulation for political ends.

The authors believed fascist tendencies in America were at an early stage in the 1940s, but warned a time might come when Americans could and would be "susceptible to ... [the] psychological manipulation" of a rabble rouser.

The authors were German refugees living in the US, with first-hand experience of the Nazi regime, which imbues their work with a "tremendous vitality and a sense of relevance".

[4] During their exile from Germany, while living in Los Angeles, Max Horkheimer and Theodor W. Adorno, both members of the Frankfurt School and working in conjunction with the Institute for Social Research, undertook an expansive research study of what they saw as a shift in spirit, a worldwide movement, which "defined not only mass culture in the United States but also the administrated cultures of the Third Reich and Stalin's Soviet Union.

"[19] Having provided his own definition for the causes of the social malaise, "as a would be leader of a popular movement" he sets goals for improvement in Chapter VII ("A Home for the Homeless"); however his solutions are found to be empty promises.

They warn, however, that under certain circumstances, such as loss of security for the middle class, America should contemplate the "possibility in which a situation will arise in which large numbers of people would be susceptible to his psychological manipulation".

[25] They found that agitators typically employ 21 common tactics in their speeches, such as characterizing the enemy as a low animal (i.e. vermin), or building up an image of a folksy "chosen leader who responds to an inner call.

"[1] They explain the successes of mid-20th century demagogues such as Gerald L. K. Smith, Carl H. Mote, William Dudley Pelley, Joe McWilliams, and Charles Coughlin.

The authors' purpose was subject appeal of these messages to a thorough analysis, to inoculate future generations of Americans against demagogues and ideologues – the "prophets of deceit".

An agitator presents himself as an advocate for social change with the purpose of defeating the underlying causes of discontent, builds a movement and proclaims himself its leader; he is "in fact, full of reactionary cliches about 'the good old days' and the 'simple American Way which our ancestors loved'."

[8] Much of the basis of pro-fascist and antisemitic propaganda appears to be irrational in substance, yet Löwenthal's research revealed that it was planned and calculated to achieve a specific response.

According to Löwenthal and Guterman, the social discontent is real, it "reflects the stresses imposed on the individual by the profound transformations taking place in our economic and social structure – the replacement of the class of small independent producers by gigantic industrial bureaucracies, the decay of the patriarchal family, the breakdown of primary personal ties between individuals in an increasingly mechanized world … the substitution of mass culture for traditional patterns.

"[29] A political agitator will manipulate existing social discontent, distortion the underlying causes, with in turn results in irrational responses and actions.

"[31] Löwenthal and Guterman demonstrate Adorno's belief that the greatest danger to American democracy is manipulation of mass culture: radio, television, and film.

[32] Harvard lecturer Charles Clavey believes the book offers the most striking insights into current illiberal movements such as Trumpism.