It is in connection with the president’s right to present a defense, not his confrontation-clause right, that Senator Paul and the president’s defenders should frame their argument that the “whistleblower” should be subpoenaed to testify at public impeachment hearings.
A cautionary note. When I was a prosecutor, I loved defense cases. They were often not very well thought through — just an effort to dirty up investigators toward no coherent end, or toss in some favorable details about the accused that were quite beside the point of the charges. A defense case can open the door to prosecutors to place before the factfinders a great deal of unflattering information about the accused that would otherwise have been excluded as irrelevant. Defense lawyers tend to be much better at dismantling the prosecutor’s case for conviction than at presenting their own affirmative case for acquittal. When a defendant proceeded with an extensive defense case, I almost always ended up concluding that it had helped me more than it helped the defendant.
Presenting an affirmative case would not be without risk for the president. If the Democrats’ case for impeachment is weak and has no chance of success, he would probably be better advised to leave well enough alone. Nevertheless, if the president wants to argue that the bureaucracy has had it in for him from the start, and has coordinated with Democrats to undermine him, he has an unusual embarrassment of riches to exploit.