Do lawyers have to be licensed for specialties?

[Stranger_On_A_Train]

Can a commercial lawyer effectively represent criminal defendants in court (Better Call Saul)?

This is a general question although it references a fictional character. In the TV Show “Better Call Saul”, the character Kim Wexler does some pro bono work as a public defender, even though her day job is as a litigation lawyer in a commercial law firm. This seems incredible to me because the roles are so different that I can’t see how she could possibly be competent to advise and represent people in criminal cases. In a US context, is this realistic?

Stranger