Kamala Harris' election would defy history. Just 1 sitting VP has been elected president since 1836

NEW YORK (AP) — As Vice President Kamala Harris begins her fall campaign for the White House, she can look to history and hope for better luck than others in her position who have tried the same.

Since 1836, only one sitting vice president, George H.W. Bush in 1988, has been elected to the White House. Among those who tried and failed were Richard Nixon in 1960, Hubert Humphrey in 1968 and Al Gore in 2000. All three lost in narrow elections shaped by issues ranging from war and scandal to crime and the subtleties of televised debates. But two other factors proved crucial for each vice president: whether the incumbent president was well-liked and whether the president and vice president enjoyed a productive relationship.

“You really do want those elements to come together,” says Julian Zelizer, a professor of history and public affairs at Princeton University. “If the person the vice president is working for is popular, that means people like what he’s doing and you can gain from that. And you need to have the two principals working together.”

In 1988, Bush easily defeated Democrat Michael Dukakis, the Massachusetts governor whom Republicans labeled as ineffectual and out of touch. Bush was otherwise helped by a solid economy, the easing of Cold War tensions and some rare luck for a vice president. President Ronald Reagan's approval ratings rose through much of the year after falling sharply in the wake of the 1986-87 Iran-Contra scandal, and Reagan and Bush worked well together during the campaign. Reagan openly backed his vice president, who had run against him in the 1980 primaries. He praised Bush at the Republican convention as an engaged and invaluable partner, appeared with him at a California rally and spoke at gatherings in Michigan, New Jersey and Missouri.