Which program provides health care coverage for us seniors? medicare social security medicaid national health insurance

It is Medicare that provides health care coverage for US seniors. This was a program implemented in the early 20th century as a response to the Great Depression, which destroyed lots of the hopes of retirement for old people. 

They made a checks and balance system to equal power within the branches. the "check" meant that one branch would watch one branch and "balance" them if they were too powerful. if you want more info on this, i would just google checks and balance system.