it goes like this

In 2016—
Trump: If I don't win the election, then yeah, I might question the results.
The left: The election is airtight and inviolable! How dare you suggest fraud is possible!
[Trump wins]
The left: RUSSIA!

In 2020—
The left: We need mail-in voting to keep people safe from viral infection.
Trump and the right: But that opens us up to massive fraud.
The left: Mail-in voting is airtight and inviolable! How dare you suggest fraud is possible!

Sigh... the left has learned nothing.