An essential test for democracies is not whether such figures emerge but whether political leaders, and especially political parties, work to prevent them from gaining power in the first place--by keeping them off mainstream party tickets, refusing to endorse or align with them, and when necessary, making common cause with rivals in support of democratic candidates. Isolating popular extremists requires political courage. But when fear, opportunism, or miscalculation leads established parties to bring extremists into the mainstream, democracy is imperiled.