Supporters hear the (real) problems he describes and a commitment to fix it. The details are where it breaks down.
Many public people who are good at what they do are amazing at flattening complex problems and making people understand and agree. Bill Clinton in his prime was capable of that -- he had a Steve Jobs like magnetic force.
If you look at some of more right-wing political people, many of them lack charisma, but use speech and body language techniques that are taught to evangelical pastors and others and are really effective in those audiences, but come off creepy to others. Kinda like how Mormons are awesome telemarketers because of skills acquired on missionary work.
Combined with the fact he may be suffering from early Alzheimer's/dementia like his father and you have present day Trump.
Kudos for trying to understand someone else.
I showed a clip of him speaking to a bunch of Indians who saw virtually nothing of him except whatever they read in TOI. (TOI and most other Indian English language papers can be thought of as being Indian branches of the cathedral, at least for this purpose.) They started by mocking him, yet they quickly quieted down and watched the video with rapt attention until the end.
After watching this video they were very much against Trump cutting off the rest of the world to Make America Great Again. As in, they were using Trump's language and accepting his premises, in spite of knowing they were wrong.
This is one of the great failings of democracy. People like Trump (or Obama, who had similar abilities) can blatantly lie or just say nothing meaningful, and people will relate to them and follow them.
Trump has what best can be called a serious addiction to praise. It his hard to imagine empathizing a narcissist but from an abstract level it isn't much different from many psychological ailments. When Trump is criticized he may appear to be strong to some but I now imagine based on watching him it is extremely painful for him.
He also tended to flatter powerful people, so the most hostile people were probably the small businesses he randomly refused to pay. Now he's made many powerful enemies during the campaign.
I have to imagine this is wildly more stressful.