Which method involved a closed-door meeting of party leaders to nominate candidates?

The method involving a closed-door meeting of party leaders to nominate candidates is known as the King Caucus. This practice was common in the early 19th century, particularly among the Democratic-Republicans, where party elites would gather to decide on presidential candidates without the involvement of the general public. The King Caucus operated under the belief that a select group of knowledgeable party members could more effectively determine the best candidate to represent the party's interests, thereby streamlining the nomination process.

This method gradually became less popular as political parties sought broader participation in the nomination process, leading to the development of more open conventions. Other options, such as the General Assembly, Electoral Committee, and Convention of Leaders, do not specifically describe this closed-door mechanism used by party leaders.