In criminal trials the rule for prosecuting and defending lawyers is the same. Never ask a witness a question unless you already know the answer. The corollary rule for defending lawyers is - if the answer to your question will incriminate your client, don't ask it, and hope the prosecutor fails to do his job.
Glenn Simpson, a former employee of the
Wall Street Journal in New York, is currently on trial in the US for having fabricated a dossier of allegations of Russian misconduct (bribes, sex, blackmail, hacking) involving President Donald Trump and circulating them to the press; the objective was to damage Trump's candidacy before the election of November 8, 2016. Simpson was called to testify before the Senate Judiciary Committee on August 22, 2017; then the House Permanent Select Committee on Intelligence on November 8, and again on November 14, 2017. So far, Simpson's veracity and business conduct face nothing more than the court of public opinion. He has not yet been charged with criminal or civil offences. That will happen if the evidence materializes that Simpson has been lying.
Simpson's collaborator in the dossier and his business partner, Christopher Steele, is facing trial in the London High Court, charged with libels he and Simpson published in their dossier. Together, they are material witnesses in two federal US court trials for defamation, one in Miami and one in New York. If they perjure themselves giving evidence in those cases, they are likely to face criminal indictments. If they tell the truth, they are likely to face fresh defamation proceedings; perhaps a civil racketeering suit for fraud; maybe a false statement prosecution under the US criminal code.
Comment: This cruder form of governmental corruption pretty much describes half of Washington in one way or another.