  We follow up on the Sterling et al (2015) discovery that nearly all polar
coronal X-ray jets are made by an explosive eruption of closed magnetic field
carrying a miniature filament in its core. In the same X-ray and EUV movies
used by Sterling et al (2015), we examine the onset and growth of the driving
magnetic explosion in 15 of the 20 jets that they studied. We find evidence
that: (1) in a large majority of polar X-ray jets, the runaway
internal/tether-cutting reconnection under the erupting minifilament flux rope
starts after both the minifilaments rise and the spire-producing
external/breakout reconnection have started and (2) in a large minority, (a)
before the eruption starts there is a current sheet between the explosive
closed field and the ambient open field, and (b) the eruption starts with
breakout reconnection at that current sheet. The variety of event sequences in
the eruptions supports the idea that the magnetic explosions that make polar
X-ray jets work the same way as the much larger magnetic explosions that make a
flare and coronal mass ejection (CME). That idea, and recent observations
indicating that magnetic flux cancelation is the fundamental process that
builds the field in and around the pre-jet mininfilament and triggers that
fields jet-driving explosion, together suggest that flux cancelation inside the
magnetic arcade that explodes in a flare/CME eruption is usually the
fundamental process that builds the explosive field in the core of the arcade
and triggers that fields explosion.
