Has any elected democrat threatened to pack the supreme court, except as a response to McConnell reversing his position now that his party is in control?
You can't compare the senate majority leader with a random anonymous twitter account.
"We are on the verge of a crisis of confidence in the Supreme Court, We have to take this challenge head on, and everything is on the table to do that." is...not.
Even still, your argument doesn't follow. Reacting to someone doing a thing you disapprove of isn't the same as instigating the thing. Your argument is that since Democrats disapprove of what Republicans did, and are considering taking action to undo and action they disapprove of, that they would have also done the act. That is very strange reasoning.
Nobody should be talking about court packing. Sitting on nominations to gain tactical advantage might be a sneaky. But it’s something that’s been done forever. Expanding the Supreme Court for political purposes would be unprecedented and breaking a huge taboo. It is not at all a proportional response.
Refusing to vote on a nominee is also unprecedented. You've yet to acknowledge that in every other case the Senate voted. This time they refused to even put it to a vote. (And some senators considered continuing it through the entire clinton presidency, were she elected, I might add)
That's also a huge taboo, and for good reason. It prevents voters from making politically informed decisions because their representatives don't have actions on which to judge.
Indeed, but to find one in an election year you have to jump back to 1881, where Hayes proposed a Justice after the election had already happened. The confirmation lapsed. President Grant proposed the same justice and he was confirmed. Worth noting, Hayes also had a justice confirmed as a lame duck (William Burnham Woods).
[Edit: I missed lame-duck Millard Filmore in 1852 the first time around also]
Prior to that you had John Tyler in 1844, who had two vacancies in the court open up in his election year. He made 9 proposals of 5 different people, one (John C. Spencer) was rejected and then later re-proposed and withdrawn, one (Reuben Walworth) was proposed 3 times, withdrawn once and postponed or lapsed twice. One was confirmed. Another was proposed twice. So this whole thing was a complete circus, but even still congress did their duty and confirmed one of Tyler's picks.
Prior to that there was John Quincey Adams who, also as a lame-duck, proposed a nominee who was tabled. In 1828.
So the precedent, insofar as there is one, is that when an election has already happened, the other party can table it. Except that more often than not, that doesn't happen. In fact, it's really only happened twice, in 1828, and 1852, and then not in 1880 despite similar circumstances. And then 2016.
And again those cases were different: Adams had already lost the election, when he made the nomination. Fillmore is maybe the closest, even though it happened later in the year the election hadn't happened yet, but Fillmore also failed to be re-nominated, so in a sense he'd lost the election in the primary.
[To be extra clear, in most of the cases where a nomination expired, the same president had a nominee confirmed later (Eisenhower, Harding, Cleveland), so it wasn't a flat out refusal to entertain candidates.
You can't compare the senate majority leader with a random anonymous twitter account.