Every major decision governing our diverse, majority-female, and increasingly liberal country bears the stamp of the United States Senate, an institution controlled by people who are almost exclusively white, overwhelmingly male, and disproportionately conservative. Although they do not represent a majority of Americans-and will not for the foreseeable future-today's Republican senators possess the power to block most legislation. Once known as "the world's greatest deliberative body," the Senate has become one of the greatest threats to our democracy. How did this happen?

In Kill Switch, Senate insider Adam Jentleson contends that far from reflecting the Framers' vision, the Senate has been transformed over the decades by a tenacious minority of white conservatives. From John Calhoun in the mid-1800s to Mitch McConnell in the 2010s, their primary weapon has been the filibuster, or the requirement that most legislation secure the support of a supermajority of senators. Yet, as Jentleson reveals, the filibuster was not a feature of the original Senate and, in allowing a determined minority to gridlock the federal government, runs utterly counter to the Framers' intent.

For much of its history, the filibuster was used primarily to prevent civil rights legislation from becoming law. But more recently, Republicans have refined it into a tool for imposing their will on all issues, wielding it to thwart an increasingly progressive American majority represented by Barack Obama's agenda and appointees. Under Donald Trump, McConnell merged the filibuster with rigid leadership structures initially forged by Lyndon Johnson, in the process surrendering the Senate's independence and centrality, as infamously shown by its acquiescence in Trump's impeachment trial. The result is a failed institution and a crippled democracy.

Taking us into the Capitol Hill backrooms where the institution's decline is most evident, Jentleson shows that many of the greatest challenges of our era-partisan polarization, dark money, a media culture built on manufactured outrage-converge within the Senate. Even as he charts the larger forces that have shaped the institution where he served, Jentleson offers incisive portraits of the powerful senators who laid the foundation for the modern Senate, from Calhoun to McConnell to LBJ's mentor, Richard Russell, to the unapologetic racist Jesse Helms.

An essential, revelatory investigation, Kill Switch ultimately makes clear that unless we immediately and drastically reform the Senate's rules and practices-starting with reforming the filibuster-we face the prospect of permanent minority rule in America.