Someone posting under the name "George Bryson," today wrote: "What James White did not say is that I offered to debate him on the very interesting question: “Does Calvin or Calvinism teach that God is the cause (by virtue of His decree) the cause of sin?[”] ... Why won’t James White debate George Bryson on such an important and relevant question. While I believe that the “cross-examination” issue is for theatrics I will happily allow James White the opportunity to cross-examine me if He will allow me to cross-examine him on this issue." (full comment)
I don't know whether it is really George Bryson ... the inconsistent use of the third and first person is a bit odd. I'm not sure why Bryson would want to limit the topic in the way that he has proposed, perhaps a better resolution would be:
"Does the Bible teach that God is (by virtue of His decree) the cause of sin?"
Debating what Calvinism teaches or doesn't teach is something that is better done intramurally among Calvinists. Debating what the Bible teaches is something that would actually edify Evangelicals of the Calvinist, Amyraldian, Lutheran, and Arminian persuasions.
But, in case, George Bryson happens to read this, I have a question back for him about his proposed resolution: "What do you mean by cause?" God is not the instrumental cause of sin, and therefore is not properly caused the "author" or to modernize the expression the "actor" of sin. The instrumental cause of sin, the author/actor of sin, is the sinner himself (whether that be a man or a fallen angel).
It is the instrumental cause of sin that bears moral responsibility for the sin. So, assuming that George Bryson is interested in the kind of "cause" that is relevant to the issue of moral responsibility, then the correct (both Biblical and Calvinist) answer to the question is "no."
If George means "cause" in some other (or in no particular) sense, the question that springs to mind is, "Why is he even asking the question?" In other words, why would it matter if God, via his decree, were an ultimate cause or a "but-for" cause of sin?
Here is a video clip from the last time (to my knowledge) that Dr. White and George Bryson debated: