What are some ways in which presidents are able to act on their own

Acting President of the United States is an individual who legitimately exercises the powers and duties of the office of President of the United States even though that person does not hold the office in their own right. There is an established order in which officials of the United States federal government may be called upon to take on presidential responsibilities if the incumbentpresident becomes incapacitated, dies, resigns, or is removed from office (by impeachment by the House of Representatives and subsequent convictionby the Senate) during their four-year term of office, or, if a president has not been chosen before Inauguration Day, or if the president-elect has failed to qualify by that date.

Acting President of 
the United StatesExecutive branch of the U.S. Government
Executive Office of the PresidentStatusActing Head of State
Acting Head of GovernmentMember ofCabinet
Domestic Policy Council
National Economic Council
National Security CouncilTerm instrumentUnited States Constitution

Presidential succession is referred to multiple times in the U.S. Constitution – Article II, Section 1, Clause 6, as well as the Twentieth Amendment and Twenty-fifth Amendment. The Vice President is the only officeholder named in the Constitution as a presidential successor. The Article II succession clause authorizes Congress to designate which federal officeholders would accede to the presidency in the event the vice president were unavailable to do so, which it has done on three occasions. The current Presidential Succession Act was adopted in 1947, and last revised in 2006. The succession order is as follows: Vice President, Speaker of the House of Representatives, President pro tempore of the Senate, and then the eligible heads of federal executive departments who form the president's Cabinet, beginning with the 

South carolina was so angry about the election of lincoln that they seceded from the union on december 20, 1860. they attacked fort sumter later, on april 12, 1861.