Complex sentence: Unfortunately, Lincoln was losing any remaining confidence he had in Hooker whose senior officers expressed to Lincoln their lack of confidence in Hooker, as did Henry Halleck, Lincoln's General-in-chief.
Split into simpler sentences: Unfortunately, Lincoln was losing any remaining confidence he had in Hooker. Hooker's senior officers expressed to Lincoln their lack of confidence in Hooker, as did Henry Halleck, Lincoln's General-in-chief.