Can Trump hand pick to a degree his 2020 opponent?

The knee-jerk seismic shift of support for the "squad" within the ranks of the Democrats based on this weekend's tweets has me wondering.

Let's say the Democratic field has narrowed to a few legitimate nominees before primary season. Given the sheer number of "orange man bad" voters who will be eager to beat Trump 2020, it seems perfectly plausible that he could rally MSM and NPC support for the weakest of the group in very short order by simply ripping that particular candidate in a series of well-timed tweets. Conversely, he could damage that chosen candidate's biggest competitor(s) by simultaneously showing support for one or more of their policy positions.

The media via its predictably negative wall-to-wall coverage has unwittingly handed him an enormous amount of power.