New Delhi, Aug. 31 -- The difficulties of the world's oldest and largest democracies, the US and India, raise a question more fundamental than how their constitutions might be 'tweaked.' Can constitutional design by itself protect democracy against those who acquire power through democratic means and then undermine the institutions that brought them to office?

Plato identified this vulnerability long ago: democracy can furnish its own destroyers with the legitimacy of the popular vote. The American founders understood the danger and constructed elaborate checks and balances to contain it. Yet, James Madison also understood that institutions ultimately depend upon the people who operate them.

No constitutional arrangement can be entirely...