"POTUS has immunity when carrying out his duties outlined by the constitution."
I'm not sure shaking down a state's election officials is outlined in the Constitution.
Assembling a team of electors with forged documents doesn't seem to be in there either.
As a matter of fact, the Constitution specifies that states choose their electors. There doesn't seem to be any sort of role for the federal government in there at all.
Each State shall appoint, in such Manner as the Legislature thereof may direct, a Number of Electors, equal to the whole Number of Senators and Representatives to which the State may be entitled in the Congress: but no Senator or Representative, or Person holding an Office of Trust or Profit under the United States, shall be appointed an Elector.