The presidential line of succession is the list that contains the names of 18 candidates who are eligible to take over the Presidents office in the event of presidential emergencies. These emergencies include events such as the sudden death, assassination, impeachment or resignation by the President of the USA. This presidential line of succession is specifically designed keeping in mind the stature of the post held by these candidates as well as their caliber to lead the nation. Only individuals who have their names mentioned in the list qualify for filing the office of the President. This list ensures that the country will never be without a President. Extract of the first section of the law has been given below for your reference: 3 USC § 19 (a) : Vacancy in Offices of Both President and Vice President; Officers Eligible to Act.

1. "If, by reason of death, resignation, removal from office, inability, or failure to qualify, there is neither a President nor Vice President to discharge the powers and duties of the office of President, then the Speaker of the House of Representatives shall, upon his resignation as Speaker and as Representative in Congress, act as President.
2. The same rule shall apply in the case of the death, resignation, removal from office, or inability of an individual acting as President under this subsection."

The presidential succession act was introduced into the US Constitution and it currently features under (3, USC section 19). The order of presidential succession was passed in 1792 during the 25^th amendment of the constitution of America, wherein it was amended again in 1886. It was further amended in 1947, after President Roosevelt's death which is still in practice. After President Barack Obama, the Vice Presidential succession comes second in the list, to take over the office of the President of the USA.

Presidential Line of Succession	People in Office (2011)
Vice President	Joe Biden
Speaker of the House of Representatives	John Boehner
President Pro Tempore of the Senate	Daniel Inouye
The Secretary of State	Hillary Rodham Clinton
The Secretary of the Treasury	Timothy Geithner
Secretary of Defense	Robert Gates
Attorney General	Eric Holder
Secretary of the Interior Affairs	Ken Salazar
Secretary of Agriculture	Tom Vilsack
Secretary of Commerce	Gary Locke
Secretary of Labor	Hilda Solis
Secretary of Health & Human Services	Kathleen Sebelius
Secretary of Housing and Urban Development	Shaun Donovan
Secretary of Transportation	Ray LaHood
Secretary of Energy	Steven Chu
Secretary of Education	Arne Duncan
Secretary of Veterans Affairs	Eric Shinseki
The Secretary of Homeland Security	Janet Napolitano

Department of Homeland Security However, the 1947 act has had to be modified several times because of the inclusion of new cabinet positions. For example, after the Twin Tower terrorist attacks in 2001, the United States Department of Homeland Security was added to the list in 2002, though; this was protested by people. The reason being, that people wanted the Department of Homeland Security to be placed higher up on the list as they believe that it is a more important office and much-needed in these times of rampant increase in terrorism. They believed that the official for disaster relief and security was more capable to take over the presidential office as compared to some other posts for example education or agriculture. Though, the bill expired with the end of the 109^th Congress and thus the office remained in the last of the list. The presidential line of succession also prohibits acting officials to be considered as suitable candidates. That is because the acting official was not selected by the panel during the selection of the 18 candidates. These 18 officials alone have the potential to take over the presidential office in case of emergency.