Well, I didn't think Bernie could beat Trump but he might have. Given the hatred for Hilary the Repubs had fostered for decades, culminating in Bengazhi, and coupled with her dismal debate performance and arrogance ("deplorables," you bet), she couldn't have beaten anyone, it seems to me.
Buttigieg has no such history. Here we have someone the Repubs only have a short time to tarnish. Let's try to picture him debating Trump. Now that would be something.