Cecil, W5DXP wrote:
"When a lot of electrons flow between the plates of a capacitor, for
instance, the voltage capability of the capacitor has been exceeded and
it is in a failure mode."

Yes. Conduction current flows when electrons penetrate the dielectric.
Capacitors consist of conductors separated by insulation. This
dielectric bars conduction up to some voltage limit where the insulation
breaks down. This insulation can be a high vacuum, but at some voltage,
a spark can jump the gap even in a vacuum.

We have vacuum capacitors, both fixed and variable. We have vacuum tubes
which have measured interelectrode capacitances. We have radio waves
which propagate as the result of alternating magnetic and electric
fields. These propagate in the high vacuum of deep space where
corpuscular particles may be speeding through like infinitesimal
bullets, but evidence is that no matter is required to allow influence
by electric and magnetic fields. An alternating electric field, even in
a vacuum where no electrons are in motion, produces an alternating
magnetic field which generates an alternating electric field, and so on
and so forth ad infinitum, ad nauseam.

We know this works as we use radio signals in deep space and view light
from the sun and other cosmic sources. It was J.C. Maxwell who
speculated that displacement current produces a magnetic field the same
as conduction current does, to explain how radiation occurs.

Best regards, Richard Harrison, KB5WZI