Lyndie - I suspect you may be able to understand the 'vitriol' here against DT. We have all been fed a fairly capacious diet of his "Tweets", randomly interpreted by various political experts to support their own subjective opinions.
His lack of diplomacy is taken by some as refreshingly forthright - others simply see it as rude.
No, our own politicians and the media are highly skilled in the area of evasion and subversion when and where it suits their personal and/or party agenda.
Your observation that -Lots of companies here are American.- is true to some extent, but the likes of say Cisco Systems, a global telecoms giant, IBM, Dell, Google, Amazon, Microsoft, etc., etc. have space in the UK, but their EMEA headquarters are inevitably in other EU countries, whether it's Ireland, the Netherlands, or elsewhere.
Whether the 'hard Brexit' occurs or not, they will still operate outwith the UK for administration and headquarters purposes, and if it becomes costly, they, like Lloyds of London may consider relocating some of their operations elsewhere in Europe.
DT's support for Brexit has nothing to do with any "special relationship" with the UK, and everything to do with the disruptive geo-political strategy both he and Vladimir Putin are deploying.