Midway through most mornings, Karen Joyner steps outside her office and walks a few hundred yards to the shelves of her Virginia food bank.

She wanders the aisles of the large, airy warehouse in Hampton. She smiles at neatly arranged rows of crushed pineapple, canned string beans, loaves of bread.

But for the past three months, those shelves have been barren. The Virginia Peninsula Foodbank, which serves roughly 150,000 people a year, is facing an unprecedented drop in donations, Joyner said, turning her daily routine into “an embarrassment.”

“I really don’t like going into the warehouse and seeing no food on those shelves,” said Joyner, the food bank’s chief executive. “I’m very worried about it.”

She is far from alone. Food banks and charities around the District, Maryland and Virginia are experiencing declines in donations — of money, of food, of clothing — this holiday season, crippling their ability to serve the needy, organizers say.

Some have launched last-minute funding drives. Others are turning to publicity campaigns, but all are growing increasingly desperate.

Experts point to a cluster of responsible factors, all piling together with stunningly poor timing: a recent change in tax code that disincentivized middle-class donations, the passing of older generations with more ingrained habits of giving and the increasing efficiency of large supermarkets, among other things.

A report released this summer by Giving USA found that charitable giving by individual Americans fell about 1 percent last year, declining from $295 billion in 2017 to $292 billion in 2018.

“Before the Great Recession, about two-thirds of American households donated to charity,” said Una Osili, a professor at Indiana and Purdue universities’ joint campus in Indianapolis who helped compile the Giving USA report. “Today about 55 percent of households donate. It’s been a steady decline.”

The drop is not evenly distributed, and it’s become more pronounced in the past few years. It’s mostly middle-class families that are choosing not to give nowadays, said Stacy Palmer, editor of the Chronicle of Philanthropy. By contrast, the country’s wealthiest citizens — buoyed in part by Republican tax breaks — are either continuing or upping their large contributions to such wealthy institutions as hospitals and universities, according to Palmer.

The trend explains why, overall, total charitable giving in the country remained essentially flat from 2017 to 2018, Palmer said. But, she added, this comforting statistic obscures an uncomfortable truth: that local and regional nonprofit organizations, which typically rely on the middle class for support, are taking a gigantic hit.

“The kinds of people who support food banks and local social services, they tend to be people who are middle class or lower class,” Palmer said. “That’s because they’re much more in touch with the needs of social services; maybe they’ve benefited themselves from a social service at some point.”

Middle- and lower-class Americans are also the demographic group most directly affected by a change in tax code in the Republican-backed 2017 tax law. In a move meant to streamline the tax filing process, that act doubled the standard deduction individuals can take on their taxes.

Unfortunately, Palmer said, this also annihilated tax benefits formerly obtained through charitable deductions.

“Now, we don’t think people just give because of the tax benefit,” Osili said. “But we certainly think it affects the amount they give.”

Cynthia Brooks, the executive director of the Bea Gaddy Family Center in Baltimore, first glimpsed the implications of the new law when she was doing her own taxes.

“For eons, I’ve been giving the same amount, giving what I can with my income level — but there was zero [tax benefits] this year,” she said. “Suddenly, my donations just didn’t count.”

Brooks watched in dismay over the next few months as donations to the center — which serves tens of thousands every year — failed to roll in. Overall, giving to the center is down by 50 percent this year, Brooks said. The decline has made it nearly impossible to pull off the Thanksgiving dinner that the center serves annually to 15,000 needy individuals around the city, she said.

Taking a break from frantic meal preparations Tuesday, Brooks said she is doing “everything she can” to make the dinner happen Thursday. But she’s still short hundreds of cans of string beans, has nowhere near enough corn and is missing brown sugar for the candied yams.

“I’ve never seen a dip like this,” Brooks said.

The tax code change is not the only reason for the decrease in giving, Palmer said — the death of older generations is likely a contributing factor. Younger Americans are less likely to donate in the traditional manner, she said, partly because they may feel more comfortable giving to individuals online through sites like GoFundMe and CrowdRise.

Millennials and members of Generation X may also view charities with greater distrust than did previous generations, Palmer said, a consequence of the “general drop in believing in any institution” that America has witnessed over the past few years.

“And then, another part of what people think is that, during the Great Recession, people just stopped giving because they couldn’t afford to — and then they never picked up that giving habit again,” Palmer said.

As they face declining donations from individuals, food bank managers are also grappling with a steep slump in corporate contributions — especially from large supermarket chains, normally a significant source of supplies. This is primarily because of two trends, said Canice Prendergast, a professor of economics at the University of Chicago.

“First, firms are getting better at estimating demand,” he said. Second, “there are a lot of chains — Big Lots, for example — that buy excess food from firms now, [so] that is a much bigger market than before.”

Joseph Mettimano, the president and chief executive of Central Union Mission in the District, said the twin drops in giving — from households and supermarket chains — led to an overall slump in donations between 5 and 10 percent at his nonprofit organization, which serves roughly 3 million meals each year. He described the situation as a “double whammy.”

“When you’re receiving both less cash and less gift-in-kind [food and clothing], ultimately it means you can do less,” Mettimano said.

Or, as Joyner put it: “We’re just so much less effective in how far we can stretch a dollar.”

For Brooks, an added woe came in July, when President Trump tweeted that Baltimore is a “disgusting, rat and rodent infested mess.” Since then, she said, some have reached out to say they’d like to donate food — but are too scared to risk a trip to the city.

“He shines such a dim light,” Brooks said. “But my city is such a good city. My city is so much better than the words in his tweets.”

Then she hung up the phone. She had turkeys to baste.