So has Mrs. Clinton’s campaign. She has proposed new tax credits for savings, tuition, health care, elder care and renewable energy use. Her retirement tax credit, for example, would match the first $1,000 saved by couples making less than $60,000. For those making from $60,000 to $100,000, the match would be 50 cents on the dollar. To Mrs. Clinton, these policies are more efficient than old-style bureaucracy and less expensive than across-the-board tax cuts.

“Her view is that it makes more sense to have government focus on specific needs and concerns,” Neera Tanden, the campaign’s policy director, says. “And her experience in the government informs that view.”

Mr. Obama  the onetime community organizer  tends to look at economic policy more like a foreign-policy realist looks at the world. He will sometimes remind aides that policies that look good on paper don’t necessarily work in the real world. “That’s his thing,” says Austan Goolsbee, Mr. Obama’s top economic adviser.

The problem with Mrs. Clinton's savings plan, according to the Obama view, is that many people won’t save even when they are offered subsidies to do so. After all, many workers who are eligible for 401(k) matching funds don’t take advantage of them now.

So Mr. Obama would instead require companies to deduct money automatically from their employees’ paychecks and place it in a savings account the employee owned. Employees could opt out of the program. But if they did nothing, they would end up saving money. It’s an idea that comes directly from academic research showing that savings rates have jumped when individual companies have adopted such plans.

Mr. Obama isn’t opposed to narrow tax credits, but his agenda isn’t organized around them. Instead, he has proposed an across-the-board $1,000 tax cut for every family in the bottom 90 percent or so of the income distribution. As he notes, the middle-class squeeze is caused by slow-growing wages and the rising cost of energy, education and health care. It’s not a narrow problem.

His skepticism about government tinkering also helps explains his stance on a health care mandate. (Except for the mandate, the Democratic health plans are essentially the same.) Mrs. Clinton and Mr. Edwards favor a mandate, because  as they point out  there will never be universal health care without one.