Sure, but the House did not subpoena him. So in the words of that Olson fellow. Why would the Senate do the House's homework? (1) But Any way, I'd like to hear from him, Hunter (2) , the WB (3) and anyone else that may shed light on the truth.
As for the procedure. It's my understanding that after the opening statements, The senate votes on witnesses. If they subpoena Bolton the WH can claim executive privilege to keep him from testifying (4). It's at that point as the third equal branch the SCOTUS would step in and decide. Am I wrong about that?
(1) I've heard this argument several times. Here's my reply:
(1.a.) The house did not subpoena him, but they did subpoena his assistant, who asked a judge to rule on it. Bolton was asked to testify; he said he would pending the judges ruling. for point of reference, Don McGhan was also asked to testify during the Mueller hearings last march. McGhan refused. They subpoenad him April 22, and finally last November the courts ruled against him. He appealed and the case is on-going. This court delay would be similar to a court challenge for Bolton.
(1.b) The Senate, including CJ Roberts, has the power to do what the House could not - get an immediate, un-appealable decision to compel testimony.
(2) The only question to Hunter that has any relevance, at all, would be this: "Are you related to the Democrat Presidential Candidate Joe Biden?" Why Hunter was employed by Burisma is none of the Senates business, nor is how much he made, or the investment strategies of his holding company. It's all completely irrelevant to whether Trump withheld aid to pressure Ukraine to smear a political rival.
(3) what could the whistleblower possibly add? Assume the whistleblower was Hillary Clinton herself - does that change anything? Does that mean we can all say, "oh, gee, it really sucks someone saw that the president was corrupt and told on him, the real crime is tattle-telling".
(4) I don't believe privilege extends to breaking the law. Withholding congressional appointed aid violated the law. Further, Trump already commented on what he talked about with Bolton (via tweet, yesterday). By doing so, he surrenders any privilege claim.