A party question for politically moderate Anglo-Saxons: which would be worse, Corbyn as Prime Minister with a substantial majority, or Trump as President?
I'm not going to answer that here. However, a couple of remarks:
(1) Prime Ministers are much more powerful than Presidents, due to the absence of checks and balances. Obama, a reasonable and essentially centrist President, has achieved virtually nothing since 2010 due to Republican majorities in Congress. Trump is a plain and simple fascist, so one would hope will face greater opposition.
(2) Trump is also known to have a very short attention span. The idea that he would have the endurance to push major law changes through is a dubious one.
(3) For that matter, Corbyn has proven consistently unable to even produce a policy platform. Imagine what he would be like if he not only had to think of policies, but put them into legalese and defend them against some former Oxford Union debating champion.
(4) Therefore, our fear of what Trump and Corbyn would be like should be rooted less in what we think either of them would do, but rather in what they wouldn't do. (e.g. defend the Baltic Republics/Falkland Islands).
(5) This fact, combined with Trump and Corbyn being the least qualified candidates for governing their respective countries since at least 1900 and 1983 respectively, ought to raise a few questions for libertarians.