In what ways has the power of the Presidency been expanded and constrained over the past several decades?
This one could go on for pages. The two major events in our history that have increased the power of the Executive branch are the Depression, and WWII.
Roosevelt instituted a number of programs (social security, welfare, etc) that should have been deemed unconstitutional by the Supreme Court.
Presidents have tended to see themselves as supreme beings - using Executive Orders, privilege and "National Security" as reasons to carry out personal vendettas (Nixon), wars (Clinton, Bush Sr & Jr) and much more. Just think - there hasn't been a legal declaration of War since 1941. Yet how many conflicts has our "Commander in Chief" engaged our men and women in, in complete contravention of the Constitution and federal law?
The Federal government in general uses the IRS, Federal Reserve, the FBI and other federal agencies to harrass, intimidate and threaten their enemies, political and social. The only recent (past 50 years) president that tried to limit the power of the federal government was Kennedy. He issued Executive Order 11110, which drastically limited the power of the Federal Reserve by giving the issuance of currency back to the Treasury, and legalized silver as a form of currency. Johnson removed this executive order after the assassination.
Johnson threatened Martin Luther King, Nixon threatened John Lennon, and the list goes on. There have been very few constraints on any Presidential action over the same period of time, primarily because the Supreme Court has been so completely packed with idiots, who are payed off to look the other way, by the last four presidents. Since Sandra O'Connor retired, the whole gang is a bunch of political hacks who could barely come up with a cogent legal opinion among the nine of them. The reason for all of this, and you can research the Bilderberg Group, and Council on Foreign Relations; is to create a world system of financial control, in private hands, able to dominate the political system of each country, and the economy of the world as a whole.