Editor: Many people blame investment banks alone for the decline in US economy over the past five years. Yet clearly, the Federal Reserve and consumers have each played a vital role in this decline. In the five years prior to the recession, the Federal Reserve kept interest rates low and consumers had a habit of spending beyond their means. Combined, consumers went ahead and took on large mortgages to buy homes they couldn't necessarily afford should they lose a fraction of their income.
In the editor's argument, the portion in boldface plays which of the following roles?