Usage and Grammar

Q. I am unsure of how to handle subject-verb agreement in sentences that involve em dashes or parentheses. For example, “The president (and, to some extent, Congress) is committed to the policy” or “The president—and, to some extent, Congress—is committed to the policy.” Is it correct to treat the subject in each of these sentences as singular or plural?

A. Singular. Choose a verb as though the parenthetical “afterthought” weren’t there. (This is true if the afterthought is set off by commas as well.)