Politicizing tragedies does seem crass and opportunistic, but the previous president did set the standard:
But here is the thing -- when Obama politicized tragedies, he had the entire Democrat media complex behind him, supporting his agenda. It was a storyline they already wanted to promote, and he demagogued it anyway. Because with Dems, the agenda comes first.
Trump has the opposite dynamic going for him. The MSM doesn't like the "Iowa teenager brutally murdered by an illegal immigrant" narrative, and would totally embargo it if they could. By tweeting about Molly Tibbett's murder, the president forces it into the public eye.
President Trump uses Twitter to go over the heads of the media. What he wants the American people to hear, they will hear.
The gatekeepers no longer control the narrative like they used to -- and that makes them seethe with anger.