How are US presidental debates controlled?

Question

Debates tend to be held at most countries right before elections. However, these are mostly traditions, and not mandated by law. For example, Romania got some criticism for not having enough of these, while in Hungary Orbán had his last debate back in 2006 (against Gyurcsány who won that time), and other countries might have similar problems.

In the US, according to the relevant wikipedia page, the constitution doesn't mandate debates. Is there any law about it, either about form (e.g. length, number of topics), or simply about its existence, or is this just tradition there as well? What happens if candidates can't agree on the rules?

Answer 1

You are correct that the U.S. Constitution doesn't demand these debates. Thus, U.S. presidential debates are usually held by third parties. For instance, the Commission on Presidential Debates (CPD) usually organizes presidential debates.

These third parties dictate the rules of these debates and usually invite the candidates to attend. To attend a debate, a candidate must usually meet some criteria to get invited. The CPD, for example created this rule in 2000 (see Wikipedia link above):

In 2000, the CPD established a rule that for a candidate to be included in the national debates he or she must garner at least 15% support across five national polls.[8] This rule has been controversial[9] as it has effectively excluded U.S. parties other than the two major parties.

Since they are held by third parties, the debate format is entirely set by the debate host. While they may take candidate's requests into account, the debate host has the final say.