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.
All about Rank in WW2. The most basic part of the Army is rank. Men are given ranks so that everyone knows who can give orders to whom, as often those orders will result in men dying. Army rank is a two tired class system: officers and enlisted men. Historically officers were the upper class; intelligent and well trained men of finer birth. Enlisted men were the lower working class, the ones that do the dirty jobs. WW2 continued the democratization of the military that had taken root in WW1.