Bernadette Daywalt had yet to decide whom to vote for in the presidential election. But the 69-year-old retiree said her decision would probably come down to economics.

She and her 82-year-old sister have struggled to keep up with rising grocery prices over the past few years, and they now frequent a food pantry in the Philadelphia suburb where they live.

“I think we’re headed downhill right now, with the cost of food, the cost of everything,” Ms. Daywalt said as she checked on her voter registration at an outreach van parked outside the Elmwood Park Zoo on a crisp October afternoon. She voted for Mr. Trump in 2016, and she felt better economically when he was president.

Ms. Daywalt’s perceptions underscore a tough reality facing Democrats, who have been trying to recapture a working-class vote that has been slipping away from them.

Many economists say Vice President Kamala Harris’s economic proposals would do more to help everyday Americans than the agenda put forward by former President Donald J. Trump. One model suggests that her package would boost post-tax income for the poorest Americans by 18 percent by 2026, much more than the 1.4 percent bump Mr. Trump’s ideas would offer.