You really have no idea do you
Are you telling me that Alexander doesn't let people down and those people don't have trust him?
Are you saying that the Irish border won't create issues?
Are you saying the SNP won't be pushing for indyref2 and that it's likely Alexander will at some point say something derogatory about the Scots, adding fuel to the fire?
If you're answering yes to any of these questions then you really ought to take a more historical evidence based approach to your thinking.
IF Brexit isn't a success you think the public that voted for it will just say "whoops, we got that wrong!". Of course not, they'll look to blame whoever put it through as doing it badly rather than admit the entire thing was flawed from the start and they made the wrong decision.
Of course IF it goes well then of course the Tories will continue to do well in future elections regardless of anything Alexander or anyone else does. Hence why I said it was the most important issue.