Trying to remember my Livy, but early on wasn’t it the intent that one council would go out with an army and the other stay at home with the other legions?
:’) There’s an old anecdote about a reader and fan of Livy who traveled to Rome just to look at him.
The Consuls were ‘elected’ in pairs, serving one year terms, couldn’t serve again, and could veto each others’ decrees. It was set up by the hereditary aristocracy which populated the Senate, to avoid sharing any real power.
Military commanders were recruited for specific crises — such as the pirate problem, which led to Pompey’s sweeping the pirates from the seas; that culminated in Augustus’ model for a permanent imperial navy, which kept the seven seas pirate-free for centuries.
The military commanders could be (and often were) relieved at the Senate’s whim, but could be kept on campaign for years if need be. The reason Julius Caesar wrote his Commentaries on the Gallic Wars was to keep Romans interested in and supporting what he was doing in Gaul, and it remains great reading.