Per Playbook:
Backstory on Raffensperger recording Trump's call:
After Graham's attempt in Nov to get him to throw it, Brad felt threatened, so he recorded Saturday's call
After Trump tweet attacked him yesterday, BR released it to WaPo & AJC
Here:

2-"It started on Saturday when Trump and his team reached out to talk to Raffensperger, who, according to an adviser, felt he would be unethically pressured by the president. Raffensperger had been here before:

3-"In November he accused Trump ally and South Carolina Sen. Lindsey Graham of improperly exhorting him to meddle in the election to help Trump win Georgia. Graham later denied it.

4-"So why not record the call with the president, Raffensperger’s advisers thought, if nothing else for fact-checking purposes. “This is a man who has a history of reinventing history as it occurs,” one of them told Playbook.

5-"“So if he’s going to try to dispute anything on the call, it’s nice to have something like this, hard evidence, to dispute whatever he’s claiming about the secretary. Lindsey Graham asked us to throw out legally cast ballots.