As far as I know, there is no historical precedent for it. It’s just a ceremonial, respect thing. I’m not innocent of it, either. I will refer to former Presidents as “President” because I feel like they’ve earned the title. I know that, technically, it’s not correct to do so protocol-wise, but I personally don’t have an issue with it. If I were to meet Bill Clinton or George W. Bush, I’d greet them as “Mr. President”, and that’s definitely not the correct terminology for a former President.
Bob Greene writes about this a bit in my favorite book about Presidents, Fraternity: A Journey In Search of Five Presidents. When preparing for his first meeting with a former President — Richard Nixon — Greene wrote:
I had decided in advance to call him “Mr. President.” Not exactly a startling choice — it’s what anyone, given a few minutes to consider it, would likely elect. But you don’t find yourself in this situation very often — at least, I hadn’t, up to that day — and coming up with the proper words had been something I’d had to stop and think about. On an elevated scale, it’s sort of like deciding how much to tip the pizza delivery guy — you’ll probably come up with the correct answer, but it does require a moment or two’s reflection.
He was no longer, of course, technically “Mr. President,” because he no longer held the office — and the circumstances of his leaving had been unlike those of any other man who had ever resided in the White House. “Mr. Nixon,” although respectful, seemed wrong on several levels, the most important of which was that I thought there was a chance I might bruise his feelings by not using a title he had loved so much. He was a formal man — always had been. Best to do this by the book.
So “Mr. President” it was.
Now, one of my pet peeves is when I see the word “President” in lowercase letters. This is a personal decision because it appears that the correct journalistic style is “president”, not “President”, unless you’re using the President’s name (such as “President Obama”). Fortunately, Bob Greene and President Nixon (see, I just did it) also refer to this in Fraternity:
I told Nixon about the exercise I had done in my head before coming to visit him — the decision about how to address him. I said that, while I knew “Mr. President” was correct, a matter of protocol, I had gone over it in my mind, even said it aloud a few times, to see if it sounded right. It’s a phrase most of never are in a position to use — it takes some getting accustomed to.
Nixon said that it was not a small matter at all — in fact, he said, he was a little upset by a practice that also might seem small to some people, but that he found significant. It had to do with the way that some newspapers capitalized the word “President,” and others used the lowercase “president.”
I asked if he thought such a choice meant much more than a stylebook flip of the coin — whether he thought there was more to it than that.
"Well, yes," Nixon said. "You have what I think is a rather juvenile practice which has occurred in the last four or five years. You do not capitalize the word "president" when you say "the president."
"Now, I’ve noted the very significant change. We still follow the British. The British started to capitalize about three years ago. Then the Wall Street Journal in this country. Now the New York Times does it. Washington Post, no. Now that, to me, is a little petty.
Apparently, he read the papers that closely — apparently, he had taken note of something that most newspaper readers might just skip over. It couldn’t be that he considered the lowercase “president” to be a personal affront to him — he was no longer President, so the stories weren’t referring to him. And even if they had been — for all the indignities he had suffered in print and on broadcasts, for all the critical things that had been said about him over the years, the capitalization style of “president,” you might think, would not be a matter of concern for him.
But it was — he told me that the lowercasing of “president” was one more sign of a growing lack of national respect for the institution of the Presidency itself. He gave no indication, as he talked about this, that perhaps other matters might have contributed to the country’s changing attitudes about the White House and the people who were elected to live there.
Instead, he said that the use in newspapers of “president,” lowercase, was very much like the idea of first families who might choose to dress casually inside the White House. He strongly disapproved of both.
Richard Nixon might have felt strongly about it for different reasons than I do. To me, it just seems right to capitalize “President” when referring to the President of the United States. Then again, I’m a capitalizer (I think I just made that word up). I’m like those people in the 1700s who capitalized words that seemed more important to them. I know that it is a problem, but I’m going to keep doing it. If you’ve ever received a text message or e-mail from me, you’d note that my capitalization, punctuation and grammar is as close to perfect as it could possibly be. It might be a sickness.