Medicare and Social Security will wax ever larger in aging Americans’ lives. Far fewer workers in the private sector are retiring with lifetime “defined benefit” pensions; many more will rely on a fragile, unstable, highly unequal “defined contribution” system of individual retirement accounts linked to stock market gyrations.

A GoBankingRates study estimates that 42 percent of all Americans (and nearly 33 percent of Americans 55 or older) will retire broke, with less than $10,000 of retirement savings. A 2016 Economic Policy Institute study found that half of all households have no retirement savings at all. For those ages 56 to 61 who do, the median was $17,000. As grim as these figures are, it is even more sobering to consider that the data was generated during the longest stock market bull run in American history. In a future market crash, stock-heavy 401(k)’s could become 201(k)’s.

In trying to blend older white voters’ interests with its younger, more multiethnic base, Democrats might study AARP’s “Be the Difference” senior voter awareness campaign. AARP’s big-tent policy advocacy seeks to balance the politics of both its current membership base of disproportionately older white moderates and conservatives with the more diverse backgrounds of younger and future members. AARP’s voter drive emphasizes multigenerational and multiethnic themes, with a core promise to preserve Medicare and Social Security for future generations. The campaign heralds vigorous outreach to African-American and Latino voters, “especially in races where they could compose a deciding voting bloc.” The messaging and imagery are tilted more toward Democratic voters, but AARP’s campaign also tries to redirect aging middle- and working-class whites’ anxieties about jobs, family difficulties and demographic-cultural change to the dangers of Social Security and Medicare cutbacks.

And Democrats need to groom new congressional senior citizen champions to make these pitches. Who is the next Ted Kennedy? Given the age of Democrats like Joe Biden, they have several strong potential candidates.

Yet Democrats must be aware of issues that can hurt them in courting older voters: Medicare for All and generous immigration reforms that would include a pathway to citizenship for undocumented populations perhaps as large as 22 million (according to a recent Yale University study).

The Brookings Institution demographer William Frey has described an already simmering “racial generation gap.” Data supports that description: A 2017 Pew Research Center poll found that young or liberal respondents (or both) substantially favor Medicare for All, while older respondents, especially conservatives, oppose the idea. Many polls also find that younger Americans have more positive attitudes toward immigrants and immigration than older whites. Those issues are related: Older Americans probably suspect (as was the case with the Affordable Care Act) that Medicare for All might produce “socialized medicine” that could shift Medicare resources from seniors to younger populations. In addition, these fears and resentments would be compounded if the resources were stretched to include millions of unauthorized immigrants who would become eligible for universal health care through citizenship.

Mr. Trump has already articulated such fears and previewed a likely Republican strategy to attack Medicare for All as a “socialist” scheme that will bankrupt Medicare: At a September rally in Montana, he said that Democrats want to turn the country into (socialist) Venezuela, destroying Social Security, and that “they say ‘Medicare for All’ until they run out of money, which will be the third day, and it will be Medicare for nobody.”