He got a lot of it from other Twitter accounts. He retweeted Heartiste at least once and for awhile followed the DemsRRealRacists parody account (now J Burton). That's how he ended up retweeting politically incorrect stuff about black crime and Israel's wall, among many other things.
In the interim he has been relentlessly advised and admonished to stay away from Twitter as much as possible. It's not "presidential", they say. Even many of his Alt Right supporters recommend this. I heard Black Pigeon Speaks say as much on a recent podcast.
A couple months into office, it looks like Trump's taken this advice to heart. While he is still fairly active on social media--though not nearly as active as he was during the primaries and the general election--he now uses it for little more than what are basically press releases. If he's a person very much attuned to what is directly in front of him, as seems to be the case, this has to have been, from our perspective, a change for the worst.
Of his children and children-in-law, Don Junior is by far the most sympathetic to the shitlord memery that helped put his dad over the top. He is, not coincidentally, the most fiery of the brood on Twitter:
|Top of Don Jr's feed at the time of this posting|
Someone close needs to convince the president to reengage on social media to fire up in the morning and blow off steam at night, critics be damned. It's something he clearly enjoys doing that includes, as a side effect, the salvation of the Western world.