Will Bolsonaro’s new Supreme Court pick be as loyal as he hopes?

That chief executives might seek to curry undue favor from the judiciary by using their power of nomination is a consistent and well-known concern. And this is the main reason why Supreme Court appointments are so intensely scrutinized. 

There are many ways that the ideal delicate balance between branches of government can be corrupted. For example, President Jair Bolsonaro has said on multiple occasions that former Justice Minister Sergio Moro joined his cabinet with the clear aim of ending up on the Supreme Court bench. Mr. Moro denies ever making such a request, either implicitly or explicitly, as doing so would have constituted a conflict of interest in his actions dating all the way back to the Car Wash investigation. 

A Supreme Court appointment can also be used as a political gesture to a given constituency. This can be especially deleterious if the gesture is meant to signify a willingness to impinge on core constitutional principles.

This is the concern with Brazil’s newest Supreme Court justice, former Solicitor General and Justice Minister André Mendonça. The Senate confirmed his nomination last week by a 47-32 margin — the tightest ever. Mr. Mendonça will be the second justice selected by President Bolsonaro. 

A Presbyterian minister, Mr. Mendonça fits the “extremely evangelical” profile promised by the president back in 2019. In policy terms, Mr. Mendonça has signaled an...