Republicans are desperate to be in a position to disqualify the Constitutionally mandated Vote of the People as being legitimate.
This is because they know it will elect Biden as President.
They won't be able to prove it's illegitimate, so they have a plan to:
1) Attempt to delay the final vote tally past the legal deadlines, while exhorting registered Republicans to vote as early as possible, and hoping the "sorry, too late" votes will be mostly those of Democrats.
Since they won't be able to prove that mail-in voting itself, is fraudulent, the tactic is to slow the mail-in process, hoping the Democrats will use it the most, so it will be primarily Democratic votes that will miss the deadlines.
2) Attempt intimidation at polling places by armed vigilante groups loyal to Trump, hoping that just the publicity about this will be enough to dissuade the more timid Democrats, who waited until Nov.3rd, from voting at the polling stations.
3) Attempt to fabricate enough of a controversy over whether the Election results showing that Trump lost were valid, in order to force the final decision into the Supreme Court.
This tactic has been used only once before in American history, in 2000, when the Republican majority on the Court refused to extend the deadline for the final recount in Florida's botched election, thereby enabling it to appoint the Republican candidate, POTUS. The fact that the final recount proved that Bush Jr. had actually lost BOTH the national Popular Vote AND the Electoral College Vote, was then of no consequence.
THIS is the reason for the Republicans' otherwise inexplicable determination to bypass the normal, always-before-used timeline for the Senate appointment of a Supreme Court Justice. They HAVE TO RUSH Amy Barrett onto the Court IN TIME to disgracefully violate the Vote of the People of the United States of America.
There's no other possible explanation for it. Barrett could have been confirmed later, with no problem when it comes to upcoming cases that are already scheduled to be ruled on by the Court.