The Senate filibuster—a procedural rule that allows 41 senators to shut the whole place down—is not in the Constitution. James Madison never envisioned the filibuster and was dead and gone before soon-to-be secessionist John C. Calhoun hatched it in the 1830s as a mechanism for blocking civil rights legislation.
The filibuster has evolved into a de facto 60-vote requirement to do essentially anything in a Senate where 51 votes would otherwise constitute a majority. Some cracks have formed in the rule since the 1970s to allow budgetary matters and judicial nominations to go forward on a majority vote, but the filibuster is otherwise intact.
Former Senate aide Adam Jentleson wants the Senate to shatter the filibuster once and for all. In his new book Kill Switch: The Rise of the Modern Senate and in an interview with The Daily Beast, Jentleson argues that obstruction was good politics for Republicans when Barack Obama was president and will be good politics when Joe Biden is president.