Was Barnswell wise?

He decides to opt out of the plot and later implies that the reason is that he didn't think it was a sure thing. So what did he think was going to happen?

That the plot was going to fail? If so, probably the first thing Scott and others would do is tell prosecutors that Barnswell was complicit in it -- or it would come out from documentary evidence -- and he would be sacked, and probably worse.

Or did he think the plot was going to succeed? But then why not go in on it? Because probably otherwise Scott and the others would punish him for his disloyalty.

Seems like by choosing neither side he committed himself to a disastrous result either way. The only thing that saved him is that the president found out and did the unlikely thing of sending someone out to get his statement, certainly the least plausible thing to happen.