  We present the first PSP-observed CME that hits a second spacecraft before
the end of the PSP encounter, providing an excellent opportunity to study
short-term CME evolution. The CME was launched from the Sun on 10 October 2019
and was measured in situ at PSP on 13 October 2019 and at STEREO-A on 14
October 2019. The small, but not insignificant, radial (~0.15 au) and
longitudinal (~8 deg) separation between PSP and STEREO-A at this time allows
for observations of both short-term radial evolution as well as investigation
of the global CME structure in longitude. Although initially a slow CME,
magnetic field and plasma observations indicate that the CME drove a shock at
STEREO-A and also exhibited an increasing speed profile through the CME (i.e.
evidence for compression). We find that the presence of the shock and other
compression signatures at 1 au are due to the CME having been overtaken and
accelerated by a high speed solar wind stream (HSS). We estimate the minimum
interaction time between the CME and the HSS to be about 2.5 days, indicating
the interaction started well before the CME arrival at PSP and STEREO-A.
Despite alterations of the CME by the HSS, we find that the CME magnetic field
structure is similar between the vantage points, with overall the same flux
rope classification and the same field distortions present. These observations
are consistent with the fact that coherence in the magnetic structure is needed
for steady and continued acceleration of the CME.
