My guess is they (DOD) are practicing defending against such scenarios.
You mean like they practiced the withdrawal from Afghanistan or how they handled January 6th. Maybe, they are practicing by allowing an assassin to get within 150 yards from Trump and get off numerous shots or hiding out in the hedgerows of one of Trump’s golf courses, in order to shoot Trump, of course the Secret Service shot multiple times from less than 10 yards and missed each time trying to take out the 2nd assassin.
Seriously, Washington DC should be locked down tight for the inauguration, recent history suggests that might not be the case.