When do Presidential candidates have to announce who their running mate is?

I was wondering when a candidate running for President of the United States is required to list who will be running with them for Vice President.

I assume there must be some sort of deadline. That a ballot cannot merely list the Presidential candidate and leave the VP slot blank and they can choose whoever they want up till the day they get sworn in.

But then I am unaware of when they traditionally do this. Whether it is at their respective conventions, when they feel like it or what.

Anyone know?

In time to get it on the ballots for all 50 states (plus DC). They have various deadlines.

Technically, they could actually leave it blank. People vote for electors, not candidates, so you could theoretically have people voting for the presidential candidate’s electors and have the electors choose the VP when they meet. That’s not likely, however.

In general, the latest it’s done is at the convention, after the Presidential candidate has been nominated. It used to be the delegates would vote on a presidential candidate, then, after he is chose, vote for the VP candidate of his choice. The conventions may have changed this.

But from a practical point of view, the choice is better if it’s done early. Candidates use the selection as a bump to get their name in the media in the month before the convention.

Another factor is that not naming a Vice Presidential candidate would allow your opponent to raise the issue of who you will pick. If John McCain for example declined to name his running mate, the Democrats could argue that he’s going to pick Donald Rumsfeld or somebody equally unpopular.

The presidential candidate isn’t required to make that choice at all. The candidate could leave the determination to the party National Convention. This was done routinely in the Nineteenth Century, but with diminishing frequency in the Twentieth (the last occurrence being at the Democratic National Convention in 1956).

Even when the candidate makes the choice, he or she is technically making a “recommendation” to the convention delegates as to whom to nominate. Until 1972 the recommendation was usually made (if at all) during the convention itself; nowadays it is usually made weeks or months earlier. This is entirely at the discretion of the presidential candidate.

And even then, it’s still just a request to the convention; they don’t actually have to follow it but of course they always do.