You can find the details here. The gist of it is this:

There’s a rule that you can’t put on evidence of prior “bad acts” to prove that a defendant committed the specific bad acts he’s being tried for in the present case.

It’s not that such evidence is completely irrelevant; it’s that it’s unduly prejudicial to the defendant. Such evidence tends to poison the jury against the defendant well out of proportion to the actual light it sheds on the current crime being judged at trial.

But that’s what the state of New York did to get their conviction. …

Another exception, which seems to be the one used in this case, is to claim you’re not putting on these witnesses to prove his prior bad acts, but to shed light on his state-of-mind he had when committing the acts he’s on trial for.

The prosecution put on three witnesses to accuse Weinstein of prior rape, and claimed they weren’t presenting this evidence just to show he’s generally a rapist, but to prove that his state in mind in the current case was one of intent to commit a sexual assault. That is, it wasn’t just a mistake where he misread the woman’s level of interest in him.

But I mean, come on: You can’t tell the jury “don’t consider this testimony as evidence that he committed the current crime, just consider it as far as his state-of-mind.” That’s telling people to put the information in a special vault in their brain that they cannot access except to answer one particular question. No one’s brain works like that, not even the brain of Noted “Compartmentalizer” Bill Clinton.

And speaking of Bill Clinton – a somewhat similar approach was used in the Paula Jones case to query him in a deposition about none other than the extent of his sexual relationship with Monica Lewinsky, and that’s what led to the entire Lewinsky story coming out in public and leading to his impeachment. I was against such questions then, and I’m against them now. To refresh your memory in the Jones case [emphasis mine]:

Jones’s lawyers decided to show to the court a pattern of behavior by Clinton that involved his allegedly repeatedly becoming sexually involved with state or government employees. Jones’s lawyers therefore subpoenaed women they suspected Clinton had had affairs with, including Arkansas Appeal Tribunal employee Gennifer Flowers, as well as White House employee Monica Lewinsky. In his deposition for the Jones lawsuit, Clinton denied having “sexual relations” with Monica Lewinsky. Based on testimony provided by Linda Tripp, which identified the existence of a blue dress with Clinton’s semen on it, Kenneth Starr concluded that Clinton’s sworn testimony was false and perjurious.

During the deposition in the Jones case, Clinton was asked, “Have you ever had sexual relations with Monica Lewinsky, as that term is defined in Deposition Exhibit 1, as modified by the Court?” The judge ordered that Clinton be given an opportunity to review the definition. It said that “a person engages in sexual relations when the person knowingly engages in or causes contact with the genitalia, anus, groin, breast, inner thigh, or buttocks of any person with an intent to arouse or gratify the sexual desire of any person”. Clinton flatly denied having sexual relations with Lewinsky. Later, at the Starr Grand Jury, Clinton stated that he believed the definition of sexual relations agreed upon for the Jones deposition excluded his receiving oral sex.

It was upon the basis of this statement that the House of Representatives voted to impeach Clinton on December 19, 1998, on charges of perjury and obstruction of justice. Clinton was subsequently tried before the Senate, where votes on either charge both fell far short of the 2/3 supermajority required for conviction.

Also, please see this post of mine about the cases against Weinstein:

Of course, the fact that one woman may have lied—or been mistaken, because perhaps she was drunk—about the nature of their sexual contact does not mean they all have lied or been mistaken. As I’ve said before, each accusation must be taken on its own merits (although few people seem to do that): even assuming that the weight of accusation indicates that Weinstein is guilty of some violations “does not mean that all his accusers are telling the truth, the whole truth and nothing but the truth.” …

With Weinstein, there are so many stories that it is easy to think that most of them must be true. But that temptation must be resisted. The trouble is that truth and falsehood can be fiendishly difficult to ascertain in cases such as this. …

Are people usually that clearly in touch with their own behavior, thoughts, and feeling around complicated situations of a sexual nature, in which fear mixes with desire to advance one’s career, and in which all of it is mixed with the liberal consumption of alcohol or other substances? The vagaries of memory are part of the problem as well, and revisionism can occur either much later or very shortly after the act in question. Regret, confusion, trauma, forgetfulness, defensiveness, rationalization—all can play into it in various ways for the alleged victim.