The goldfish that I bought you on Tuesday has died. Commas are the simplest, most effective way to indicate a nonrestrictive element , and the reader who can trust a writer to use them properly needs no guidance from the choice of pronouns. That was the weapon that did the damage. In this example, once again, the difference may appear minuscule. That which lives must die.
Good writers use a comma or commas to indicate a nonrestrictive element.
Philandering presidents who abuse their office should be impeached.