The struggle in the Senate over which witnesses, if any, to call in the impeachment proceedings against President Donald Trump have been centered, from the Democrats’ perspective, on John Bolton and a handful of lesser administration role players. Meanwhile, Republicans have focused on former Vice President Joe Biden’s son, Hunter.

Both sides have overlooked the most central witness, who actually could help their position — or hurt their opposition’s: the president himself.

It’s customary for the defendant or accused in most legal proceedings to testify, or at least be afforded the option. It has seemed eminently sensible to do so in this case.

The president has the most germane information on what happened with the Ukrainian situation and, for that matter, the resistance to congressional cooperation, which form the two grounds for his impeachment.

As a compelled witness by the Democrats, he could not claim executive privilege for what he did and why and how. Nor could he assert a Fifth-Amendment constitutional privilege against self-incrimination because this is not a criminal proceeding. He and his acolytes repeatedly have uttered the mantra that no crime was committed.

If Trump refrains from being called as a witness by Democrats, his defense team should summon the president as its witness, which could be helpful to its cause by allowing him to explain why his telephone call with his Ukrainian counterpart was, as he so often has described it, “perfect.”

Democratic House managers also could benefit by being able to question him under oath and in the glare of the public. They also would relish the opportunity to cross-examine him about his telephone call to show that it was imperfect — indeed, improper.

This form of questioning of an adverse witness is called, in legal jargon, impeaching the witness.

Marshall Tanick

Minneapolis

The writer is a constitutional law attorney.