I was able to get to the command line using Ctrl+Alt+F1.
Then, I was able to follow one user's instructions on this thread.  It was not necessary to recover the system from USB.
In your /home/ubuntu/ folder there will be a folder NVIDIA-INSTALLER containing the release.  Go to this directory and extract it.
sudo -i
tar xvjf Tegra124_Linux_R19.3.0_armhf.tbz2
Do the following to change the LDK ROOTFS DIR (not sure what that is, but this works ...)
export LDK_ROOTFS_DIR=/
echo ${LDK_ROOTFS_DIR}
Go to the Linux For Tegra directory and run this script:
cd Linux_for_Tegra
./apply_binaries.sh
Confirm your success (I got all OK's):
sha1sum -c /etc/nv_tegra_release
On sudo reboot my GUI loaded after a slightly longer than normal black screen (for suspense obviously).