I reckon, or willfully hope, that even that woman I mentioned meeting (fervent islamophobe) has plenty of potential to be disappointed by trump. She kept saying 'give him a chance'. Maybe by the time the next election comes around she will feel that he let her down and will be open to alternatives. I think that's very possible.
Yes - some people who voted for Trump are already regretting this - the "I didn't believe he would
really defund Planned Parenthood!" and the "He said he'd drain the swamp but cotdamn, he's just put more corrupt rich people in it," types. Others may regret it in future, when their health care coverage is axed, the promised jobs never come, they're caught in a big public health outbreak/natural disaster and help doesn't come, etc. If they take their heads out of their fundaments long enough to understand why these things happened (no, it wasn't the Chinese, the Muslims, the gays or God punishing everyone for not being faithful enough,) they will figure out how NOT to vote GOP next time.
The problem is though, when the result of the Trump administration and Republican congress' actions bites a Trumpite/Tea Partier in the butt, they will do anything possible to believe that something else is to blame, not their ideology and not their leaders. We've already seen how Trump voters have eagerly swallowed stories peddled by Breitbart, InfoWars, etc., so it won't be that hard to cook up some garbage they'll believe instead of facts.
I don't know if you met the woman in the UK, but I'm confident there will be Trump supporters who visit, tour London or wherever, even talk to local people, but still go back home believing the very same tripe about Londinistan, Sharia law, gay couples kissing on every corner or whatever it was they believed before they came.
You've got to remember when it comes to fundamentalist Christians, belief for them is everything. Whatever they see, do, hear or experience, if it contradicts the teachings of their church and their faith, it will be rejected. They will accept the most preposterous explanations for things they read, hear, see or even experience first hand, so long as it means they don't have to question their belief. Doubting leads to sin. Sin leads to Hell. Also, lose your faith can mean being rejected by your church, your community, even your family. I suspect some who's faith isn't 100% bone fide stick to the script for this reason.
Fundamentalist Christians form a huge block of Trump supporters, and they apply the same faith they have in God to their faith in their political leaders. Reaching out to them is a waste of time.