I found an excerpt on the prohibition of Chanufa at http://ayproject.com/members/PDF/set4lesson21.pdf
Here is an excerpt:
Flattery of a Sinner
Anyone who sees another Jew violating an issur and flatters him, whether with
words or some gesture that indicates his approval, or even if he remains silent and
does not reprove him for the sin, has transgressed not only the mitzvah of
tochacha, but also according to some opinions the prohibition of flattery, derived
from the passuk: “V’lo Sachanifu es Ho’oretz asher atem bo, Do not sully the land with flattery” (Bamidbar 35:33). By implying that we approve of the sinner’s
misdeeds, our allegiance to HaShem comes under question, since a servant
cannot love his master if he loves his master’s enemies.
Flattery that is prohibited includes: praising resha’im (wicked ones) or wickedness,
praising someone in a way that will cause him to sin or will reinforce his error,
“buttering up” someone so that he will trust you and you can then deceive him,
and praising your child or other relative when he or she is doing wrong.
Undue Flattery to Agripas and Those Similar to Him
It is stated in tractate Sotah at the end of chapter 7 that at the time when King Agripas was reading the verse, “You may not appoint a foreigner”, etc. [Deuteronomy 17:15] tears dripped from his eyes because he was not from the seed of Israel. They said to him, “you are our brother”. Now at the same time Israel became liable to extinction because they unduly flattered Agripas. For even though they didn’t have the ability to protest, nevertheless, they should have been silent and not strengthen him in this way [by saying you are legitimate, you are our brother]. And this is the punishment of one who gives undue flattery in the matter of a transgression because he is afraid of the other person and is not concerned about the fear of the Holy One Blessed be He [until here is the translated quote of the Mishna Brura chapter 156].
In “Agripas Situations” – Mishna Brura implies, silence is an option but strengthening the sin is not.
Halachos of Rebuke
for additional situations where silence is an option.
One might ask, why have I chosen to focus on the Sabbath observant politicians who sends words of encouragement to “Gay Pride” events or praises those individuals who are fighting to make abominations, acceptable in the eyes of the general public.
My answer is that most people when they are honest with themselves understand that secularists make up their moral standards based on what type of system of actions and prohibitions ends up helping, themselves, their friends, and their allies.
It has no real claim to be moral, more than the other guy who sets of friends, interests, and allies leads him to hold an opposite view on morality.
The Sabbath observant individual is expected to be the representative of an objective Biblical morality, as opposed to the “jokers” who are just blabbing about their personal set of likes and dislikes. So when the Sabbath observant politician says something which strengthens evil it is a bigger blow to the truth, It is much more likely to confuse people about what is really right and what is wrong.