I just came across the following sentence in the fourth Catilinarian oration (Cicero, In Catilinam 4,22):
Quamquam est uno loco condicio melior externae victoriae quam domesticae, quod hostes alienigenae aut oppressi serviunt aut recepti [in amicitiam] beneficio se obligatos putant; qui autem ex numero civium dementia aliqua depravati hostes patriae semel esse coeperunt, eos cum a pernicie rei publicae reppuleris, nec vi coercere nec beneficio placare possis.
Although in one point the circumstances of foreign triumph are better than those of domestic victory; because foreign enemies, either if they be crushed become one's servants, or if they be received into the state, think themselves bound to us by obligations; but those of the number of citizens who become depraved by madness and once begin to be enemies to their country,—those men, when you have defeated their attempts to injure the republic, you can neither restrain by force nor conciliate by kindness.
(Translation by C. D. Yonge.)
This does not seem to be a particular common expression, although the meaning "matter, point" for locus is documented. On the other hand, you cannot go wrong by riffing off Cicero.