In 2012, candidates needed either one percent or 500 signatures (whichever was lower) from Democrats in each of the state's 50-plus congressional districts. They had two months to do so -- which, particularly if you're hoping to keep expenses under $5,000, is a time crunch. Other states work similarly; some don't.
A contemporary definition of rank-and-file is prevalent in labor union vernacular when referring to general membership and not union leaders. Rank-and-file generally means the employee doesn't occupy a high-level position within the organization.
A shelf file is a cabinet designed to accommodate folders with tabs on the side rather than on the top. The cabinet has no drawers, only shelves. Some shelf files come with doors that recede into the cabinet. These cabinets are typically 12 or 18 deep, for letter or legal size folders respectively.