Pennsylvania's mail ballot results don't look right

All of the major networks started confidently predicting yesterday that Joe Biden would win Pennsylvania after all the mail-in ballots that had been received by the state had been counted. The numbers gurus at the networks reported that Biden was capturing 78% of the votes from mail in ballots, and Trump 21%. In other words, Biden was winning this vote group by 57%,

This margin seems too high, based on the party registration of those whose mail in ballots have been confirmed.  

The party registration data suggests that Democrats were 65.5% of those who returned mail ballots, Republicans 23.4% and independents 10.4%. If independents split their votes evenly, then one possibility was that Biden would win this voter pool by 42.1%, the difference between their 65.5% share of registered voters who returned mail ballots, and Republicans’ share of 23.4%. Let us then assume that independents broke heavily for the Democrats, say 80-20, Then Democrats would have about a 48.3 % lead, 73.8% to 25.5%. Let us further assume that more registered Republicans shifted to Biden than registered Democrats to Trump, so that the real margin was 50%.
 
How does the Biden victory margin change with different shares of the mail in vote?
  • At 42.1% (50/50 split of independents returning mail ballots),  Biden wins this pool of 2,506,507 by 1,055,260
  • At 48.3% (80/20 split of independents), Biden wins by 1,210,667
  • At 50%, Biden wins by 1,253,279
  • At 57%, the margin reflecting the state’s announced results, Biden wins by 1,428,737
It is almost certain that Biden will win the state when all voting ends by fewer than 175,000 votes. If the mail in vote split were not 57%, as announced, but something more consistent with the party registration of voters who sent back mail in ballots, the change in the margin for Biden among this voting group  is a reduction  ranging from 175,000 to 373,000 votes in the  three scenarios with different vote margins from 42.1% to 50%. Is there a good explanation for why Biden would win this voting population by so much more than the registration numbers suggest?  I do not see it. 
 
Count me skeptical of Biden’s margin of 57% among mail in ballots, and his soon to be declared  “victory” in the state, which will elevate him to President elect with more than 270 Electoral College votes.

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