The democratic party is the impeached the president during his last year, over circumstantial claims that didn't pan out. It was at that point that the gloves came off. Game set match.
Hillary Clinton herself has said so, something along the lines of "you must fight like your life depends on it for your values." The left was doing it, now the right is doing it.
The only skill required is managing to pull the cover over the eyes of your constituents while you take money from invested interests.