From two expert presidential scholars comes a new answer to why the Trump presidency happened: decades of partisanship and policies have centered the president as the sole focus of American government to create a treacherous system whose danger may far outlive the politics of Donald J.Trump.The election of Donald J. Trump on November 6, 2016, changed how we understand the American presidency—but this transformation was not of his own making.His unprecedented rise to power led to an administration where Trump brazenly defied established constitutional norms and institutions.Yet, as Nicholas F. Jacobs and Sidney M. Milkis reveal, Trump’s presidency was not merely a shocking departure from tradition, but a symptom of a constitutional disease that had has long afflicted the American polity.They call this condition presidentialism, a dangerous shift towards an executive-centered politics and government that places immense power in the hands of a single individual. While some scholars of American politics view the Trump presidency as a cult of personality, Jacobs and Milkis argue that his unsettling ascent to the White House was decades in the making, the result of numerous cultural, institutional, and constitutional changes.From aggressively redeploying the federal government’s administrative powers, to using the tools of the modern presidency to undertake a hostile takeover of the Republican Party, Trump’s presidency reveals the peril of a presidency-centered democracy that combines executive aggrandizement and polarizing struggles over the meaning of American identity.The disruptive features of the Trump presidency should not be viewed as an ephemeral phenomenon, nor does Donald Trump’s departure from the White House end the threat that presidentialism poses to American democracy. Subverting the Republic explains why the Trump presidency happened—and why it might happen again.