The Imperial Gardener and The Widow Of Georgios by Sean M. Brooks.
"'Does Molitor imagine we'll never get another Olaf or Josip on the throne?' the Gospodar rumbled. 'A clown or a cancer...and, once more, Policy Board, Admiralty, civil service bypassed, or tyrannized, or corrupted. If we rely on the Navy for our whole defense, what defense will we have against future foolishness or tyranny? Let the foolishness go too far, and we'll have no defense at all.'
"'Doesn't he speak about preventing any more civil wars?' Kossara ventured.
"Bodin spat an oath. 'How much of a unified command is possible, in practical fact, on an interstellar scale? Every fleet admiral is a potential warlord. Shall we keep nothing to stand against him?' He stopped. His fist thudded on a rail."
-Poul Anderson, A Knight Of Ghosts And Shadows IN Anderson, Sir Dominic Flandry: The Last Knight Of Terra (Riverdale, NY, 2012), pp. 339-606 AT p. 408.
They nearly do have another Olaf on the throne because, later, Olaf Magnusson tries to overthrow Gerhart! But we gather that there was an Emperor Olaf - and that he was a clown?
A bad Emperor can bypass, tyrannize or corrupt the Policy Board, the Admiralty and the civil service; a fleet admiral can become a warlord. The Pax is precarious.