I feel like I should be saying more against Donald Trump's presidential bid

But, in reality, why?  If at this point in time you are still undecided about this election, then nothing I can say will sway you.  I understand not being enthused about Hillary Clinton, but that's just not relevant.  Donald Trump is in no way fit to be President of the United States.  If the idea of casting a vote for him is not abhorrent to you, then you have an issue that talking about politics won't solve.