I know this is an impossible question, the future is chaos, but we can at least identify and discuss some key factors.
When I say "successful leftist revolution" I mean one that happens soon enough to prevent, or have non-negligible odds of preventing, the collapse of human civilization as we know it due to climate change.
In all likelihood I think we're fucked as far as climate change is concerned, but we should still try to improve our odds. There's no prize for correctly predicting that we're fucked.
What about the last 4 years has associated Trump with "effective"? He couldn't even invade Iran or coup Venezuela. Whereas if it was Hillary, Maduro would have been Gaddaffi'd already.
in a nutshell: fascists can get bold under Trump. Trump himself isn't the threat.