It's not that i trust President-elect Trump; he exemplifies distrust and the fomenting provoked by it.
A national policy must not be naive, but at the same time, the transparency and authenticity of trust must be evident in the people who execute public policy.
President Obama, i could believe; Mr Trump, not so much; I hope he changes this low public expectation.
About the letter, i suspect you're right as to it enacting any change in The Donald; nevertheless, the Public should voice its expectations without equivocation, imho. Here's our chance.
btw, what's said above applies also to heavy-handed religious rightists.