The small-scale turbulent dynamo (SSD) is likely to be responsible for the
magnetisation of the interstellar medium (ISM) that we observe in the Universe
today. The SSD efficiently converts kinetic energy ${E}_{\mathrm{k}\mathrm{i}\mathrm{n}}$ into magnetic
energy ${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}$ , and is often used to explain how an initially weak
magnetic field with ${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}\ll {E}_{\mathrm{k}\mathrm{i}\mathrm{n}}$ is amplified, and then
maintained at a level ${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}\lesssim {E}_{\mathrm{k}\mathrm{i}\mathrm{n}}$ . Usually, this process
is studied by initialising a weak seed magnetic field and letting the
turbulence grow it to saturation. However, in this study, using
three-dimensional, non-ideal magnetohydrodynamical turbulence simulations, we
show that the same saturated state can also be achieved if initially ${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}\gg {E}_{\mathrm{k}\mathrm{i}\mathrm{n}}$ or ${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}\sim {E}_{\mathrm{k}\mathrm{i}\mathrm{n}}$ . This is realised
through a two-stage exponential decay (1. a slow backreaction that converts
${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}$ into ${E}_{\mathrm{k}\mathrm{i}\mathrm{n}}$ , and 2. Ohmic dissipation concentrated in
anisotropic current sheets) into the saturated state, for which we provide an
analytical model. This means that even if there are temporary local
enhancements of ${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}$ in the ISM, such that ${E}_{\mathrm{m}\mathrm{a}\mathrm{g}}>{E}_{\mathrm{k}\mathrm{i}\mathrm{n}}$ , e.g., through amplifications such as compressions, over a long enough
time the field will decay into the saturated state set by the SSD, which is
determined by the turbulence and magnetic dissipation. However, we also provide
analytical models for the decay times and utilise wait-time statistics from
compressive supernova events to show that if the magnetic field is enhanced
above the saturated state, it will not have enough time to decay the field
before the next supernova event. Hence, unless there exists a mechanism for
destroying magnetic fields that is not in our non-ideal MHD models, the
amplitudes of interstellar magnetic fields may also be a... (abridged).