It's like, if your "alibi" witness is your spouse but you refuse to let your spouse testify under the spousal privilege, the jury can infer you're full of crap.
That's not exactly right. There are, at least in NY, 4 elements here.
2. Witness testimony is not, like, repetitive of other testimony.
3. Witness is under the "control" of the party blocking them, and could otherwise be expected to testify in favor of blocking party.
4. Witness is available.
1. Bolton is material.
2. Bolton has 1st hand testimony not given by others.
3. Bolton is a GODDAMN TRUMP APPOINTEE AND ROCK-RIBBED REPUBLICAN
4. Bolton is STANDING RIGHT THERE.