America is entering a period of prolonged austerity. The entitlement commitments made by past generations have been rendered untenable by demographics and health cost inflation. The problem is no one’s particular fault, but it is very, very large. Failing to get our borrowing under control would deny our children the lives we have had in this country.

This readjustment has begun to change the tenor of politics, which is increasingly focused on the distribution of painful burdens. It used to be that a budget compromise between Republicans and Democrats meant that both sides got what they wanted — tax cuts and spending increases, respectively — and that neither had to pay for it. Now compromise has to involve both sides losing something — through tax increases and spending cuts — and neither getting the political upside. This is what it means to run out of money.

The politics of austerity is inherently divisive. Some are judged worthy; others are found lacking. It becomes disturbingly easy to turn group against group. Divisions can arise by class. The top 1 percent of earners take home about 17 percent of national income. They currently pay about 37 percent of federal income taxes. Does the 99 percent want them to pay 40 percent? More?

What burdens should be imposed on the vote-rich middle class? Or the conflict can become generational. In 1970, federal spending on Social Security and Medicare was about 20 percent of the budget. By 2030, it is projected to be 50 percent. Is it fair for those who are younger and poorer to provide dramatically increasing subsidies to those who are older and wealthier?

It is a marvel that anyone should strive and sacrifice to be a legislator in a period of austerity. Perhaps it weeds the field to the most cynical and the most public-spirited. A few demagogues thrive by feeding divisions and then leading factions. But the best leaders in lean times share certain attributes:

A sense of proportion. Good leaders focus the most attention on the things that matter most. In our case, the main problem is not simply public spending — it is entitlement programs on a path of accelerating, unsustainable spending. Those who devote their main attention to cutting food stamps or soaking the rich are grinding ideological axes, not confronting fiscal realities.

The courage to take on large interests. If the largest voting bloc or the most organized pressure group always prevails, then public benefits and burdens become a function of political influence, not need or merit. So politicians, at various points, will be required to resist AARP and Americans for Tax Reform, public-employee unions and tea party activists.

A sense of humanity. Cuts that are equally applied are not equally felt. The reduction of a malaria program that saves the lives of children is not the same as the reduction of a highway program. Across-the-board cuts are an attempt to avoid political choices, but they do not avoid human consequences.

These leadership attributes come to mind with the approach of World AIDS Day on Saturday. Foreign assistance is an illuminating example of the challenging politics of austerity. It is particularly easy to highlight the division between citizens and non-citizens and impose burdens on those who do not vote in U.S. elections. Sen. Rand Paul (R-Ky.) has made the most of this argument — opposing not only security assistance in troubled regions but also all foreign aid.

There are many substantive responses to Paul’s critique of aid. U.S. foreign policy would not be particularly American if a commitment to universal human dignity did not play some role. And acting according to that commitment has traditionally been an important element of U.S. influence — shaping our image and serving our interests.

But Paul’s crusade against aid is most notable as a failure of leadership. It lacks proportion, since the total of humanitarian assistance amounts to less than 1 percent of the federal budget — an expenditure irrelevant to the United States’ long-term, structural fiscal challenge. Paul is appealing to a narrow element of the conservative coalition rather than encouraging serious conservative reflection on public problems. And he is targeting some of the most vulnerable people in the world for ideological, rather than fiscal, reasons, attempting to undermine bipartisan, humanitarian achievements on AIDS, malaria and other issues that have saved millions of lives.

This is the ultimate challenge of austerity politics: to reduce the size of the government without dishonoring the values of the nation.