It's their playbook. It has worked before and worked well elsewhere. This is their color revolution. Since they failed at undermining his support, labelling him, bringing him down through scandal or financial impropriety, they resorted to the Nixon strategy. He was ahead of them every time and released the call transcript which shut down Schiff (I gloated, I must say).
After the 2016 and 2018 election cheating was observed and countered [They] had no choice but to resort to traditional ways of cheating at the ballot box. [They] needed COVID to create the need for mail-in ballots. Here we are.