Well, they also violated an unwritten rule and several laws when they prosecuted a former President on contrived charges.
There are no “norms” for Democrats, only for (idiot) Republicans.
A better and more easily answered question is what norms have they not violated.
They started filibustering circuit court nominees in 2001 for the first time in US history.
They then tried filibustering Alito when he was nominated.
The senate GOP got so fed up with the constant filibustering of Bush's nominees, they threatened to change the filibuster. Democrats claimed that it took 67 votes to change the filibuster rule.
In the summer of 2007, then Majority Whip Schumer said the democrat senate would not allow Bush to appoint any more justices to the Supreme Court.
From Scott Brown's win in 2009, the GOP begin filibustering Obama's nominees. The democrats, having admitted to lying about needing 67 votes to change the filibuster, eliminate it with a simple majority vote.
2014, the GOP retakes the senate and slows the confirmation of Obama's nominees.
In February 2016, Scalia dies. The GOP senate refuses to give Obama's nominee a hearing, just as Schumer said the democrat senate would do to Bush in 2007.
Democrats lie again, claim this is unprecedented, despite it happening nearly a dozen times in US history.
In 2017, for the 2nd time in US history, someone nominated to move to the Supreme Court is filibustered. The GOP changes the rule, and Gorsuch takes a place on the SCOTUS.
In 2018, Justice Kennedy retires, and Trump nominates Brett Kavanaugh to take his place. The democrats run a smear campaign against him, hoping they can retake the senate in the 2018 election and leave the seat open. It doesn't work, and Kavanaugh takes his seat.
In September 2020, Justice Ginsburg dies, and Trump nominates Barrett to take her place. Democrats are infuriated, despite the fact that had they won the senate in 2016, there would have been a 17-day window with Majority leader Schumer and President Obama, when they would have rammed a nominee through.
Democrats then swear they'll pack the court when they get a small house majority, a 50-50+1 senate, and the presidency.
After massive amounts of violence by his thug supporters he was elected and promptly wrecked the economy so badly that it took almost three decades and not one but two gold rushes to fix. He allowed his thug supporters to loot the government, appointed the worst supreme court justices ever and used the Constitution for toilet paper repeatedly.
That was Andy "Ol Crook" Jackson.
As a party is planted, so it grows.
Every Which Way They Can
Right turn, Clyde!
Anytime someone claims an elected President (always a Republican, BTW) is violating some made-up "norm", it's time to reach for your wallet or your rifle.