As per the AP Style:
The AP Stylebook holds that you should capitalize president only as a formal title that is before one or more names. For example,
- President Barack Obama
- Presidents George W. Bush and Bill Clinton
President should be lowercase is all other uses. Example,
- The president will make an announcement tomorrow.
- I am now announcing my candidacy for president.
- Roosevelt was president during the Great Depression.
Also, in the specific question where this is currently an issue, the original had the capitalization as lower case and a subsequent edit changed it. I reverted that part of the edit. And then the person who made the original edit restored it with the following edit reason:
please stop insisting on the diminutive capitalization. A 'President' is not only a title of the office, it is also a branch of government. 'president' of what? A "US president" of the Senate maybe? That would be the Vice President.The diminutive 2000 spelling introduces confusion if nothing else.
- It is incorrect to say that a "President" is a branch of government. The presidential administration might be. Certainly the executive branch that the president leads is. But the presidency is not. It is the title of a specific office holder and should only be capitalized as part of the name.
- "President" of what? The country of course. But note that the style guideline posted previously uses the president of the United States in every example but only capitalizes it when used with a name.
- When used for a president other than the head of the US government (e.g. a corporate president), the same capitalization rules apply. Capitalize as part of a name. Don't capitalize otherwise.
It's also problematic in my opinion that the person who made the edit did so after already knowing that there was a conflict. In my experience, the rule is that if an edit has been reverted, the next step is to take it to Meta, not to edit war. We shouldn't be trying to argue in edit comments.
Further, in case of controversy, the default should be to go with what the original had. In this case, that was lower case. So we should only change that if the evidence is overwhelming that it is wrong and not just a stylistic choice. There is no such evidence in the case of capitalizing the letter in that circumstance. There is such evidence in favor of not capitalizing it.