Secret Services resources were diverted to Jill Biden's event and away from Trump's because they followed agency protocol applying to Trump as a former president, according to two sources within the Secret Service community.
There were also many supplemental agents from different field officers (not Trump's regular detail) providing security at the rally because Trump's regular detail has been overworked (some working 7 days straight), and only two counter-snipers.
But Trump is not just a former president -- he is the first in modern history to have run for president again -- and he has been the focus of several prosecutions and controversies (understatement intentional).
Who made the decision to divert the resources to Jill Biden's event?
Correct. It was a setup from the very top.