Both reject mechanisms to limit spending on Social Security and Medicare — and each supports his own version of “health care for all” (although Trump has issued contradictory statements).

Both reject the use of super PACs to raise large political contributions and are convinced that politicians in Washington have sold out to powerful interests that contribute huge sums to campaigns.

The similarity between the two candidates was highlighted at a televised town hall in South Carolina on Feb. 17. Mika Brzezinski, the MSNBC host, asked Trump to identify a candidate who fit the following description:

The candidate is considered a political outsider by all the pundits. He’s tapping into the anger of the voters, delivers a populist message. He believes everyone in the country should have health care.

This candidate, Brzezinski continued,

advocates for hedge fund managers to pay higher taxes. He’s drawing thousands of people at his rallies and bringing in a lot of new voters to the political process, and he’s not beholden to any super PAC. Who am I describing?

Trump replied: “You’re describing Donald Trump.”

“Actually,” Brzezinski declared, “I was describing Bernie Sanders.”

The uniting of the Trump and Sanders electorates under a common banner in a future election has strong appeal, especially to Democrats on the left.

“For decades I’ve believed, and voter research bears out, that there is a great majority of Americans who would flock to vote for a progressive who runs on a populist economic message and talks in simple terms,” Steve Rosenthal, president of the Organizing Group, a political consulting firm, and former political director of the A.F.L.-C.I.O., wrote in response to my email inquiry:

Cobble together Trump’s older, less educated, lower income, white soft-Republicans, Independents and his less hard-line conservative voters with Senator Sanders’s younger, white, less than $100K family income, Dems and Independents — along with historic Democratic base constituencies and you’ve got a potent formula for success. The candidate is fighting first and foremost for American jobs, is pro-choice, supports marriage equality and makes raising wages central to her/his campaign — speaks truth to power in a blunt way — and is real. Sign me up.

Jill Lepore, a professor of American history at Harvard, writing in the Feb. 22 issue of The New Yorker, also describes the similarity of the Trump and Sanders campaigns:

The people who turn up at Sanders and Trump rallies are wed, across the aisle, in bonds of populist unrest. They’re revolting against party elites, and especially against the all-in-the-family candidates anointed by the Democratic and the Republican leadership: Clinton and Bush, the wife and brother of past party leaders.

This unrest has been unleashed, in part, by the information technology revolution of the past several decades, Lepore writes:

None of the candidates, not even the party favorites, are campaigning on behalf of their party; most are campaigning to crash it.

The “party system,” Lepore continues, “like just about every other old-line industry and institution, is struggling to survive a communications revolution.” The “ill effects” of the revolution

include the atomizing of the electorate. There’s a point at which political communication speeds past the last stop where democratic deliberation, the genuine consent of the governed, is possible.

While there are obviously striking differences between the supporters of Trump and Sanders, Troy Campbell, a professor of marketing at the University of Oregon, argues that:

Many, but not all, Trump and Sanders supporters have similar concerns and are drawn to a similar candidate with a change-preaching, anti-Washington, entertaining, take-no prisoners, apologize-for-nothing personality. More and more Americans are becoming less identified with a party and more generally anti the political establishment. This anti-political-elite sentiment runs deep in both the Sanders and Trump community.

Sean Trende, senior elections analyst for RealClearPolitics, noted that Senator Sherrod Brown of Ohio might be the kind of politician who could appeal to voters on both the left and the right. Brown, Trende said, “holds a longstanding skepticism of trade and has more blue collar appeal than I could see Elizabeth Warren having.”