Tevi Troy explains in a Wall Street Journal column why Americans are electing the ultimate crisis manager when the cast their presidential ballot.

The cam­paign has been un­usu­ally focused on ex­actly the char­ac­ter­istics that are es­sen­tial in a time of cri­sis: hon­esty, calm­ness, re­solve. Un­for­tu­nately, the two ma­jor-party can­di­dates are lack­ing in im­por­tant ways. Mrs. Clin­ton’s email scan­dal and re­cent ob­fus­ca­tions about her health un­der­mine her cred­i­bil­ity with the Amer­i­can peo­ple, which is the ba­sis for ef­fec­tive lead­er­ship in a dis­as­ter. With­out it, lead­ers can­not count on get­ting peo­ple to fol­low dif­fi­cult di­rec­tives dur­ing a cri­sis.

In 1976, for ex­am­ple, Pres­i­dent Ger­ald Ford em­barked on an am­bi­tious plan to vac­ci­nate “every man, woman, and child in the United States” against a wor­ri­some strain of swine flu. Ford made sure to be photographed re­ceiv­ing the vac­ci­nation him­self, but most Amer­i­cans did not fol­low suit. Only about a quar­ter of the pop­u­la­tion went along with the pres­i­den­tial di­rec­tive, which was canceled a few months later when the vac­cine was linked to cases of Guil­lain-Barre syn­drome.

Why did so many Amer­i­cans buck Ford’s in­oc­u­la­tion pro­gram? One reason may have been the loss of pres­i­den­tial cred­i­bil­ity fol­low­ing Richard Nixon’s res­ig­na­tion, which pro­pelled Ford into the of­fice. Luck­ily, that swine-flu strain was not as deadly as feared. But if a more vir­u­lent pathogen re­quir­ing mass vac­ci­na­tion were to emerge, would Mrs. Clin­ton or Mr. Trump have trou­ble per­suad­ing most Amer­i­cans to fol­low instructions?

An­other vi­tal as­pect of cri­sis lead­ership is ob­tain­ing the facts be­fore speak­ing and choos­ing words carefully—both ar­eas where Mr. Trump strug­gles. Dur­ing a dis­as­ter words that are in­suf­ficiently mea­sured could cause panic or con­fu­sion. During an­other swine-flu out­break in 2009, Vice Pres­i­dent Joe Biden said on the “To­day” show that he “would tell mem­bers of my fam­ily, and I have, I wouldn’t go any­where in con­fined places now.” It was a care­less statement that threat­ened to drive peo­ple away from air travel and pub­lic transporta­tion. White House Press Secretary Robert Gibbs had to walk back the re­marks.

In the early stages of a cri­sis, the wis­est ap­proach might be to say noth­ing. Im­me­di­ately af­ter the 9/11 at­tacks, Pres­i­dent George W. Bush was con­fronted with a press corps ea­ger for de­tails on what had oc­curred and what would hap­pen next. But con­flict­ing sto­ries were ram­pant and con­fu­sion still reigned. Press Sec­re­tary Ari Fleis­cher held up a makeshift sign for the pres­i­dent, not vis­i­ble to re­porters, with the words “DON’T SAY ANY­THING YET.”