SAN FRANCISCO — On the presidential campaign trail, Jeb Bush proclaims that Uber fulfills the American dream of self-sufficiency, while Hillary Rodham Clinton suggests Uber raises “hard questions” about the financial security of a modern job. Rand Paul extols Uber for revealing the obsolescence of government regulation, while Martin O’Malley argues that it exposes the need for new labor laws.

After upending the American taxi industry and ushering in a new era in the on-demand economy, Uber, a ride service, is now becoming an unexpected proxy in the campaign for the White House. It has center stage in the emerging debate between the left and the right over the future of work, the responsibilities of employers, the virtues of technology and the necessity of workplace regulation.

In a race already dominated by the stalled fortunes of American workers and growing income inequality, Uber is standing in as an accessible symbol of the economic aspirations and anxieties of Democrats and Republicans, in the way some practices of the giant retailer Walmart embodied them eight years ago.

“It’s becoming a lightning-rod, wedge issue that candidates have to address,” said Steven Hill, the author of a coming book about Uber and the so-called sharing economy. “It has real and symbolic importance about the direction of our economy.”