Is character assassination of witnesses allowed?

Question

Say that one side of a trial brings a witness Walter onto the stand. If the other side doesn't like Walter's testimony (and wants the jury to not take it seriously), are they allowed to engage in character assassination of Walter? For example, airing his past crimes, his controversial social media posts, etc.. To be clear, there is nothing material against the content of Walter's testimony. All they're doing is "factually" berating his character.

As a follow-up, when cross-examining the witness Walter, is the attorney allowed to proceed down a line of questioning designed solely to twist the knife on the character assassination angle (as opposed to questioning about the actual testimony that was made)? For example, directly asking Walter about controversial tweets they made supporting Nazism, as opposed to anything relevant to the case.

I'm not sure what the correct answer might be. On one hand, knowing that the witness has been untrustworthy in the past is pertinent information to be considered by the jury. On the other hand, focusing on a witness's unsavory beliefs is a massive and immaterial distraction that puts personal bias over actual facts.

Answer 1

It is allowed to introduce evidence that impeaches the credibility or reliability of a witness, which could include his previous 5 convictions for perjury. This does not constitute "character assassination", so I'm not sure what you mean by that. A felony conviction can be admissible (assuming he was not exonerated). There are limits; for example, evidence of religious belief would be inadmissible, likewise holding an unpopular political belief. The evidence has to be connected to the witness's honesty.

Answer 2

Essentially, this is allowed if the line of questioning is relevant to the case at hand. For example, if the suspect of a crime is Jewish, then the identifying witness's support of a neo-Nazi organization might be relevant on cross as it would impeach the witness's reliability as they would be more likely to be biased in their identification of the suspect.

However, if there is no racial/religious component to the case, then being a neo-Nazi has no more bearing than being a Democrat or a Communist. The opposing council would likely object on the grounds of "relevance" to which the cross-examining council will have to explain to the judge why the line of questioning is relevant or the judge will sustain the objection and instruct the cross-examiners to cease lines of questioning.

This will likely be brought up in pre-trial hearings as the side that is introducing the witness will likely want to bury the witness's political beliefs. If a judge makes a court order limiting the scope of questioning from discussing the witness's beliefs, then asking questions of this nature could get the attorney in question a charge of contempt of court.