Because presiding over the counting of the votes is one of the very few duties the Constitution allocates to the VP, so is covered under this new doctrine. He has the absolute right to conduct that how he sees fit, without regard to whether he is upholding his oath to the Constitution or not, and any conversations he had with the President are part of that duty, and similarly protected. If it turns out he is not upholding that oath, the only remedy is impeachment. (And finding 67 Senators to agree to convict.)
How can that be constitutional?
Because presiding over the counting of the votes is one of the very few duties the Constitution allocates to the VP, so is covered under this new doctrine. He has the absolute right to conduct that how he sees fit, without regard to whether he is upholding his oath to the Constitution or not, and any conversations he had with the President are part of that duty, and similarly protected. If it turns out he is not upholding that oath, the only remedy is impeachment. (And finding 67 Senators to agree to convict.)
Absolute power, just as the Founders intended.
Which, I guess, includes blackmailing the VP if necessary. To protect the president from blackmail.