The 2016 election campaign is mortifying millions of Americans in part because the presidency has become far more dangerous in recent times. Since Sept. 11, 2001, we have lived in a perpetual emergency, which supposedly justifies routinely ignoring the law and Constitution. And both Donald Trump and Hillary Clinton have signaled that power grabs will proliferate in the next four years.

Politicians talk as if voting magically protects the rights of everyone within a 50-mile radius of the polling booth. But the ballots Americans have cast in presidential elections since 2000 did nothing to constrain the commander in chief.

President George W. Bush's declaration in 2000 that America needed a more "humble" foreign policy did not deter him from vowing to "rid the world of evil" and launching the most catastrophic war in American history. Eight years later, Barack Obama campaigned as the candidate of peace and promised "a new birth of freedom." But that did not stop him from bombing seven nations, claiming a right to assassinate American citizens, and championing Orwellian total surveillance.

Mr. Bush was famous for "signing statements" decrees that nullified hundreds of provisions of laws enacted by Congress. President Obama is renowned for unilaterally and endlessly rewriting laws such as the Affordable Care Act to postpone political backlashes against the Democratic Party and for effectively waiving federal immigration law. Both Mr. Bush and Mr. Obama exploited the "state secrets doctrine" to shield their most controversial policies from the American public.