Gadol (original), the choice is between the mazik we know and mazik we don’t know. I agree that T might do something bad, just by the nature of his unpredictability. At the same time, we see what B does and he, and his advisors, will continue doubling down on the same failed policies. Our (both US and Yidden) enemies know his game as well, or better, than we do and will continue taking strategic advantage. I think you are fair enough to admit that.
Like in drasha of a boiling frog, we are being boiled slowly and predictable. Or, mixing the metaphors, the bankruptcy happens gradually and then suddenly. It is statistically worth taking a chance at T’s mix of unpredictable policies. Most encouraging, he was a similar unpredictable risk in 2016, and performed above expectations (at least, yours but mine also). Is he a bigger threat now, when he knows how to govern and has grudges? Who knows? The debate showed that he can hold himself in and talk reasonably. And I think enough undecideds (maybe 1% of voters) agree with this, so it is either T or a substitute player.