President Trump’s Friday morning tweetstorm about former FBI director James B. Comey has led to speculation that the Trump administration has taken a page from Richard Nixon’s playbook by surreptitiously recording conversations inside the White House.

As it happens, Nixon wasn’t the only president to record his conversations. Six American presidents — from Franklin Delano Roosevelt to Nixon — taped at least some of their conversations. President Ronald Reagan and his successors had several meetings videotaped.

There are a number of reasons presidents might want to have their conversations recorded. Sometimes these reasons overlap.