Those incidents happened decades ago, with a very different composition on the court. We currently have a majority of Republican-appointed judges, with several of them appointed under very contentious circumstances. And recent history shows them more than willing to play politics.
Depending on the poll, Trump has an approval rating of anywhere from ~80-95%. I'm pretty sure that constitutes his 'base'.
That would be incredibly dumb.
Lets say the democrats decide to wait until after the election to proceed with impeachment, to let all the subpoenas play out in court. Trump engages in illegal activities to fix the election (extorting Ukraine to interfere, perhaps allowing Russia to continue its activities). It tips the balance in favor of the republicans again.
So, the democrats impeach. And 'win'. And they are STILL left with a republican president, who continues to have the authority to nominate right-wing judges, issue executive orders that push a racist agenda, etc.
Much better to, you know, make sure any election is FAIR. i.e. not subject to illegal manipulation by Trump and the republicans, rather than to try to take action AFTER the election is finished.