I think it matters because of the optics. The MSM will have a field day if Graham carries through with his threats. They'll be turning the witch hunt accusations on them to us instead. Not that they'd have anything positive to say about Trump anyway......
I contend it makes ZERO difference. If he calls witnesses they'll say it proves they need to disprove something. If he doesn't they'll call it a coverup. If he calls witnesses they'll be the wrong ones, too many, or too few.
You can tell the motivation of people when they're proven wrong. After Mueller confirmed everything Trump said, the Democrats and MSM didn't apologize and admit they were wrong, because being right wasn't there objective. Attacking Trump was.