nullo tumultu publice concitato, 'without any official summons to arms.'
per me, 'by myself,' i.e. by my own exertions without calling in other help. Cf. [1. 28] 'hominem per te cognitum,' [4. 24] 'per se ipsum praestare.'
quod est primum, etc. 'Since I cannot yet venture to take the course which is the most obvious, and the most suited to the authority I hold and the strict traditions of our ancestors.' Imperium is the consular authority (not 'empire'). Cf. [2. 3] 'huius imperii severitas.'
ad. Greek πρός. 'With respect to.' Cf. [2. 18] 'adquirere ad fidem.'
sentina rei publicae, ('the refuse of the state'), forms a single expression upon which the explanatory genitive 'tuorum comitum' ('consisting of your comrades') depends.
faciebas, 'were just doing,' 'ready to do.'
exilium. See [on §20] below.
domesticae turpitudinis refers especially to family scandals, such as the story of his wife and son ([§14]). privatarum rerum dedecus, to offences extending beyond the family, but still confined to private life, i.e. having no political object.