I think a candidate's stated policy position during an election is overrated as an indicator for everything to do with their actual politics after the election. Obama's 2008 website was full of plans and ideas that never came to pass (Gitmo is still open), while his signature piece of legislation, Obamacare, wasn't even mentioned on said wesbite in any detail when he was running. I think ever since at least Reagan voters vote based on personality, team/tribe mentality, and personal affinity for the candidate. People have learned that campaign promises are bullcrap, so it's better to vote for the person you like more.
The "way things are supposed to work" guide to being a good citizen is a book that has been outdated for decades. Watergate ruined the public trust that undoes the important of politician truthiness (to steal an awesome word) that is laid out in OP.
Those upset about Trump getting elected would be better served trying to rally the troops for the midterms in two years. All this bellyaching about civic life not being what they thought, or people not voting for "the right reasons," or even complaints about the electoral college denies the reality that Obama once benefitted from everything that Trump has benefitted from. When Obama changed his mind to follow a changing America (say on gay marriage) that was applauded by the left because the shift was in a direction they like. In comparison it feels like pure hypocrisy when they bash Trump for wanting to move away from his stated policy positions (especially when many of the left hated those positions).
Time to live in the real world and get out of the ivory tower.
While I more or less agree for your nutshell summary of what motivates voters in their choices, simple logical inference would suggest that the largest number of voters, supplied with the most complete and accurate information and fact, applying their brains with the most rigorous inferences and assumptions -- would be the only basis to merely assure a chance of a wise decision.
Of course, the entire idea of a "democracy" could only guarantee temporary legitimation of authority -- nothing much more than that. But people subscribe to the myth that a majority decision is the best decision for all reasons other than that one. Anybody who entered their adult life thinking that talent or excellent performance should be the only criterion for success and ignoring the value of simply being a "good person" should wake up and see why that's not such a bad balance of attributes.
Second, I think you fail to distinguish a politician's changing opinion justified by an explication of his own logic (such as Obama's acceptance of gay marriage), versus the telltale signs that there is no logic, that there is no policy, no belief, no willingness to connect and explain what was said in the past with what is said now -- and neither honesty nor integrity of any kind.
The OP got my hackles up by an assertion that Medicare and Social Security would simply be "eliminated." A couple years ago, I was sitting in a coffee-shop recounting experiences in my earlier life as a career civil servant by day and college professor by night. Another man sitting with an evangelical minister became blustery and louder -- apparently directing his anger at me. He remarked that "They'll all be dead, anyway," referring to Social Security.
I wish I'd just stood up, walked over to him and slapped his face -- embracing arrest for assault.
There is a lot to worry about here. You cannot trust Trump in anything he says, except as he provides a megaphone for the low character and intellect of his most ardent supporters.
"Wo ist Klaus von Stauffenberg wenn Sie ihn brauchen?"
In other words, if the OP's worst-case scenario occurs, it will be like the Fuhrer's personal execution of Ernst Rohm -- figuratively. The seniors who support this toxic piece of filth will be betrayed.
And Pence isn't worth a Shilling.