President Donald Trump has a math problem.

Given his strategy to govern mostly for his base, Trump must walk an electoral tightrope to win in November. He cannot afford to lose voters motivated by economic issues. He also cannot afford to lose seniors, who supported him in 2016 by a nine-point margin over Hillary Clinton.

The coronavirus pandemic forces him to choose one. He can't have both.

Unless science develops a miracle breakthrough, Trump must choose which to prioritize: saving lives or saving livelihoods. The sooner the economy reopens, the more people will die. Those deaths will not be randomly distributed: Older voters will be overrepresented among the casualties.

That fact is not lost on the United States' older voters. By a 6-to-1 margin, Americans 65 and older say it is more important to address the spread of the coronavirus than to focus on the economy. That makes sense. A premature reopening could kill them. If Trump leans too much into an economic message that is inextricably tied to serious public health risks, he will fall off his narrow path to victory.

According to a Josh Kraushaar analysis of recent polling in the National Journal: "In mid-March, seniors were more supportive of Trump than any other age group (plus-19 net approval). Now, their net approval of the president has dropped 20 points and is lower than any age group outside of the youngest Americans."

If that collapse of support persists into November, Trump won't just lose; he'll lose in a landslide.

Conversely, leaning fully into extended lockdowns would cause him to fall off the other side. In 2016, despite his multiple bankruptcies and countless failed business ventures, voters saw him as a better choice for managing the economy than Clinton. His campaign planned to ask voters the perennial presidential election question: Are you better off now than you were four years ago?

Until recently, the answer for many — especially those invested in the stock market — was "yes." Within the past six weeks, however, 30 million Americans have lost jobs. Few have confidence that their pensions or other investments are safe. And the economic damage done by the lockdowns will hang like a millstone around Trump's neck as he makes his precarious march toward reelection.

For other presidents, there would be viable solutions to this dilemma. They could rise to the challenge of the crisis, using their presidential gravitas to unite the country behind them. (Indeed, many state governors have done precisely that, achieving sky-high ratings that Trump can only dream about.)

But Trump is temperamentally incapable of rising to meet the moment. He is bent on portraying himself — a rich, powerful man with access to top-notch health care — as the real victim while broke families go to food banks and broken families bury their dead. On Sunday evening, Trump claimed that he has been treated worse than Abraham Lincoln, who was assassinated.

Every other modern president has tried to reach out to independents and some persuadable voters from the opposition party. Trump has deliberately avoided doing so, putting base consolidation above coalition expansion. As a result, there is no wiggle room. There is no safety net waiting below his electoral tightrope just in case the worst happens.

And now it has.

Media analyses of Trump's reelection prospects often ask the same question: Will this latest scandal, this latest tweet, this latest historically devastating unemployment report finally break his stranglehold on his base? That's the wrong question, because the answer is always "no." When President Richard Nixon resigned in disgrace, one in four Americans still supported him. Trump's base, like Nixon's, consists of true believers. To them, Trump can never be worse than the system he rails against, the press he loves to hate or the Democrats that he insists are out to destroy America.

In 2016, Trump expanded beyond his base partly by winning over voters who cared most about the economy and winning over older voters. Now Trump cannot win one of those blocs without alienating the other. Meanwhile, presumptive Democratic nominee Joe Biden, well-liked by seniors, can hit his opponent on the economy and his mismanagement of the public health crisis without estranging anyone except Trump's most hard-core base.

Trump's campaign is likely to use every trick in the book to try to make Biden as politically toxic as Trump is currently. But right now, the 2020 election looks like a simple math problem and Trump's winning coalition is unlikely to add up again.

Brian Klaas is an assistant professor of global politics at University College London, where he focuses on democracy, authoritarianism and American politics and foreign policy. He wrote this for The Washington Post.