It was quite possibly the understatement of the year. Senate Majority Leader Mitch McConnell, in a Bloomberg Politics podcast last week, said Donald Trump “doesn’t know a lot about the issues.”

Trump isn’t a blank slate, exactly. He wants to ban Muslims from entering the United States, deport 11 million undocumented immigrants and build a wall to keep Mexicans out. He wants less open trade. And while he opposes gun control, he’d ban gun sales to anyone on a terrorism watch list.

But Trump’s thinking on a host of other issues — the details on taxes, federal budgets, deficits and debt, income inequality, the cost of child care, charter versus public schools, housing, student debt and many other things supposedly on voters’ minds this year — isn’t clear.

Does it matter? Where is it written that a presidential nominee has to have a passel of policy proposals to get elected? Nowhere, say several presidential historians.

The pressure to win votes by showing a close familiarity with the issues took hold after World War II, with the rising prominence of television and radio news. The first televised debates in 1960, between John F. Kennedy and Richard M. Nixon, made fluency on government policy a prerequisite for winning the presidency.

“Policy has become a profession in a way that was inconceivable before the New Deal,” says Sean Wilentz, a professor of history at Princeton University and author of several books about U.S. presidents.

But even the New Deal’s architect, Franklin D. Roosevelt, was vague when he was running for president in 1932 about how he would pull the U.S. economy out of the Great Depression. His predecessor, Herbert Hoover, was so badly wounded that any Democrat was sure to beat him. “The key was that he was not Hoover,” says H.W. Brands, a professor of history at the University of Texas and the author of numerous books on presidents, including one on FDR.

And, of course, some presidential candidates short on solutions but long on biography made it to the White House after World War II.

Dwight D. Eisenhower, for example, had never served in office and clearly “was not a policy wonk,” Wilentz says. Yet in 1952, on the back of his World War II leadership, Eisenhower handily beat Adlai Stevenson, an intellectual who had served in many government jobs, including as governor of Illinois.

When historians and pundits search for antecedents for Trump’s major-party candidacy, they go way back most often to Andrew Jackson, the U.S.’ first populist president and a real estate baron in his day.

Jackson’s campaign in 1828 consisted mostly of name-calling. Among other things, Jackson accused his opponent, President John Quincy Adams, of being the czar’s pimp while serving as the U.S. ambassador to Russia. Adams’ side accused Jackson of massacring Indians — and eating some for breakfast the next morning.

While in retrospect it’s clear how different philosophically Jackson and Adams were, you might not have figured that out reading warring newspaper accounts of the time.

Even the greatest presidents offered less substance than we appreciate today. “Abraham Lincoln kept his mouth quite shut on the big issue of his day: What would he do about the secession that Southerners threatened?” Brands says. In fact, “he kept his mouth shut clear till his inauguration.” But because the Democrats had split, his victory was guaranteed by the electoral arithmetic.

Modern-day nominees have gotten away with being vague about policy, too, says Julian Zelizer, a professor of history at Princeton University. Ronald Reagan had a few big ideas — attacking Communism, cutting taxes, shrinking government — yet was often criticized for a lack of specificity. His 1980 opponent, President Jimmy Carter, failed to convince voters that his detailed policy knowledge would serve voters better, says Zelizer, who has written political biographies of Carter and President Lyndon B. Johnson.

In 2000, Vice President Al Gore had a tough time pinning down George W. Bush on what he would do if elected. Bush got tripped up occasionally on the names of foreign leaders and the nuances of policy. But because he had been governor of Texas, few doubted that he held strong views on the issues and would put together a government to pursue those goals.

Contrast this with Trump. Not only does he avoid laying out the details of how he would fix the problems he has promised to solve, “he is defiantly uninterested in policy,” Zelizer says.

Trump instead seems to be imitating popular culture, Zelizer says, and its fascination with the antihero — such as Walter White, the teacher-turned-meth dealer in “Breaking Bad” or Don Draper in “Mad Men.” Much like the villains we root for, he is “unlikable but emotionally relatable,” in Zelizer’s description.

This persona helped Trump defeat 16 Republican rivals during the primaries, and he probably assumes it will work well against Hillary Clinton, too. In this light, his belittling, ad hominem attacks that ignore Clinton’s many 10-point white papers make calculated sense.

So does Trump’s insinuation that President Barack Obama sympathizes with Islamic terrorists. “If the incumbent or his party has been discredited sufficiently, the challenger can run a successful, content-free campaign,” says Brands, whose most recent presidential biography is “Reagan: The Life.”

The lesson for the presumptive Republican nominee? Who needs detailed policies when name-calling works just fine. So far, anyway.

Paula Dwyer is a Bloomberg View columnist.

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