Castiglione in "The Book of the Courtier" attacks flattering courtiers.These poisoned the fount of public good, the prince of Renaissance royal courts. In another form, possibly in the form of "advisers", confidants or media gurus, they are a menace to modern leaders.
As background, Castiglione's ideal "prince" is someone full of justice, self control, strength, wisdom, generosity, religion and mercy. God protects rulers who do not seek their own self glory or power. If a prince seeks to resemble God in goodness and wisdom and serves Him by distributing "for the benefit of mankind" the gifts that God has given a country, he or she will share His blessings.
This kind of ruler will be a star on earth, by making good laws and maintaining justice, supported not by ideology - but by God-given reason. God shares his character of righteousness and justice with such princes - His qualities which Castiglione says are a clearer evidence of His divinity than the light of the sun, or the motions of the planets.
If I were David Cameron or Barack Obama, I would keep the "Book of the Courtier" close by me. I would learn from it that the greatest and trap of rulers are deceitful "courtiers", flatterers, possibly others in one's own party, who lie, and lie in wait, for their own advantage, calling white, black and black, white.
They do this not out of love for their leader, but for their own status and gain. They are siren voices to whom a leader must remain deaf. Those who really love an erring ruler tell him, or her, the truth to their face.
Is it because all power corrupts, or because there are few souls of such Christian calibre today that it is often the final criticism of a failed leader that he or she has "lost touch with the people".This really means that they have lost touch with the truth, and in doing so, their own destiny.
William Shakespeare likened court flatterers to dogs, who "spaniel" rulers at their heel. He hated them not merely because of their power over the ruler, but because of their lack of love for their people and their country, which ultimately they would ruin.