Now is the time in my opinion, but I'm not going to pretend that it's not without risk, nor is it without pain.
The thing with a governmental official though, is they shouldn't be making these decisions from their own morality, but from the morality and scenario of those they represent. I don't disagree with your ideas. I mostly had a problem with the idea that trade deals should be scoffed at over morality. That's precisely the line of thinking that emboldens the right, because they (often correctly) are looking at the economic outcomes of such policies with the understanding that everyone is affected by the economy, not just those protesting or those disagreeing.
In this case, I think it's time that people that believe in human decency should be stepping up. They should be protesting, and annoying Trump. And that includes politicians!
But everyone has something to lose, and with your own Brexit, losing the US as a trade ally may well be a terrible decision for a large number of British citizens...I respect the choice to not risk that. Sometimes a decision made with the best intentions leads to more suffering all around. This could easily be a case like that.