  We present the evolution of the X-ray emission properties of the magnetar 1E
1547.0-5408 since February 2004 over a time period covering three outbursts. We
analyzed new and archival observations taken with the Swift, NuSTAR, Chandra
and XMM-Newton X-ray satellites. The source has been observed at a relatively
steady soft X-ray flux of $\approx$ 10$^{-11}$ erg cm$^{-2}$ s$^{-1}$ (0.3-10
keV) over the last 9 years, which is about an order of magnitude fainter than
the flux at the peak of the last outburst in 2009, but a factor of $\sim$ 30
larger than the level in 2006. The broad-band spectrum extracted from two
recent NuSTAR observations in April 2016 and February 2019 showed a faint hard
X-ray emission up to $\sim$ 70 keV. Its spectrum is adequately described by a
flat power law component, and its flux is $\sim$ $7 \times 10^{-12}$ erg
cm$^{-2}$ s$^{-1}$ (10-70 keV), that is a factor of $\sim$ 20 smaller than at
the peak of the 2009 outburst. The hard X-ray spectral shape has flattened
significantly in time, which is at variance with the overall cooling trend of
the soft X-ray component. The pulse profile extracted from these NuSTAR
pointings displays variability in shape and amplitude with energy (up to
$\approx$ 25 keV). Our analysis shows that the flux of 1E 1547.0-5408 is not
yet decaying to the 2006 level and that the source has been lingering in a
stable, high-intensity state for several years. This might suggest that
magnetars can hop among distinct persistent states that are probably connected
to outburst episodes and that their persistent thermal emission can be almost
entirely powered by the dissipation of currents in the corona.
