Former President Donald Trump’s key defense in the Manhattan criminal hush money case is unlikely to hold up, said former federal prosecutor Joyce Vance on MSNBC Friday — because there’s an easy way for prosecutors to defuse it. Specifically, it’s a defense laid out by former Trump attorney Joe Tacopina in conversations with MSNBC’s Ari Melber — that Trump really wasn’t making a hush payment to adult film star Stormy Daniels at all, and it was a legitimate legal expense to his former attorney and fixer Michael Cohen, who says that in reality he was the middleman to conceal the whole arrangemen…