Not american either, but I followed it. During the nomination race, Trump had already been confirmed as the Republican nominee. There was various polling done while the Democrat race was still up, and Sanders polled quite a bit more likely to defeat Trump than Hillary. Which obviously turned out to be the case. So I don’t know how certain your “strongest candidate” statement is. Polls are not facts, but it seemed to indicate something there that the leadership of the Dems ignored.