Final answer:
In the United States Senate, each member can debate a postponed main motion indefinitely due to the tradition of unlimited debate on legislation, also known as a filibuster.
Step-by-step explanation:
In the United States Senate, there is a tradition of unlimited debate on legislation. This means that a legislator can delay or prevent a vote on a piece of legislation by insisting that there is still more to debate, a practice commonly referred to as a filibuster. Any member can invoke a filibuster for any reason, so there is essentially a de facto supermajority requirement for legislation to pass in the United States Senate.