Susan Ross tells David Rosen that she likely won't become president because Grant would need to be both impeached and prosecuted first, yet the impeachment itself would remove him from office, without prosecution being a necessary step. In fact, the Department of Justice has a rule or convention that a sitting president cannot be prosecuted, and must first be removed from office.
When Mellie sighs during her divorce negotiations with Fitz, causing him to ask what else she's thought of to ask for, her mouth doesn't move.