In U.S. Presidential primaries, the Democratic and Republican parties (the largest political parties in the United States) nominate an official candidate to run during the general election; which takes place on the first Tuesday in November. From January through June every four years, each of the 50 states hold elections (also known as primaries or caucuses) to determine how many delegates (party representatives) each candidate receives. Delegates are determined by the percentage of the popular vote received by each candidate; with each state and party having different allocation rules.
Senator John McCain (Arizona) is the presumptive nominee for the Republican Party. (Candidates are officially nominated by the delegates at the national party conferences which usually take place between July and September.) Accordingly, Clinton and Obama currently receive most of the media attention as they are still fighting for the nomination. With the Pennsylvania primary on April 22, this New York Times article examines the tactics used by the Democratic candidates.