This reader illuminates how behind I am on the latest research on Charlemagne. I plead guilty. NRO readers are awesome:

Dear Jonah
I enjoyed your column on Pope John Paul 2nd, and was interested by your
allusion to Leo 3rd and the Imperial coronation of Charlemagne. I think your
point is right, but in despite of your assertion that Leo was ‘forced’ to
crown Charlemagne.
There is strong evidence that Leo sprang the coronation on Charlemagne
precisely so that the imperial crown was seen to be the gift of the papacy,
and thus in a world where the divide between spiritual and temporal power
was somewhat murky give the Papacy very important powers over and above the Holy Roman Emperor.
That Charlemagne aspired to this title is beyond doubt, that he wanted it
conferred and therefore approved by the pope is I believe unlikely – rather
he would have rather taken it himself in the manner of other Emperors and
thus avoided the ‘notion that even kings were answerable to a higher
authority’.
I could try and make this a relevant and interesting email by cross
referencing the desire of Charlemagne to abjure all higher authority – and
his chagrin when a politically astute pope out manoeuvred him – with the
modern liberal reactions to the demise of the late Pope, but to be honest I
was really motivated by sharing a somewhat esoteric thought.
Best regards – and apologies for consuming time probably better spent
mulling over the challenges of social security reform or other such modern
matters!