Here are three related questions today’s infants might find on an American history final examination when they reach college age two decades from now:

Which was a more important political dynasty in American life, the Kennedy dynasty or the Bush one? Did either the Kennedys or the Bushes leave behind a coherent philosophy of government? Which dynasty left a deeper mark on the American character and memory?

Let’s start by acknowledging that the Kennedys are in eclipse now. The senior lion of the clan, Sen. Edward M. Kennedy, is a year away from age 75; he’s clearly never going to be president. His son, Patrick, is a congressman from Rhode Island but is unlikely to reach the top of the greasy pole of politics. His nephew, Joseph III, once a promising congressman from Boston, is out of politics. Soon the Kennedys will do what the other important political family of Massachusetts, the Adams family, did: Pass into history.

Bush story isn’t over

The Bushes aren’t finished yet. George W. Bush has nearly three more years in office. His brother, Jeb, is governor of Florida and may have a national role in his future, perhaps as a vice presidential candidate in 2008. There are more Bushes coming. The Bushes are still a work in progress.

Though there are no right answers to really good final examination questions – they leave the respondent ample room to explore the evidence and reach his own conclusion – I’m going to begin by arguing that the dynasty numbers favor the Bushes. They count one ambassador (George H.W. Bush), one congressman (George H.W. Bush), one senator (Prescott Bush of Connecticut), one vice president (George H.W. Bush), two governors (Jeb Bush and George W. Bush), and two presidents.

The Kennedys don’t do badly, of course. They have one ambassador (Joseph Kennedy Sr.), one lieutenant governor (Kathleen Kennedy Townsend), three congressmen (John, Patrick and Joseph III), three senators (John, Robert and Edward) and one president. But two presidents is a very important achievement – enough, in my mind at least, to give the nod to the Bushes, and that doesn’t even count the possibility that they’re not finished yet.

Bushism hard to define

Now let’s examine the legacies, a task that’s harder to accomplish than it might seem. Indeed, in trying to define Jacksonianism, Sean Wilentz, the Princeton historian, wrote: “Even Lincoln, the most eloquent president in American history, never presented a thorough account of what ‘Lincolnism’ was, borrowed freely from his counselors, and often stood accused of inconsistency and vacillation.”

We might say the same of Bushism. It is vigilant against aggression abroad, to be sure. It is inclined toward market solutions of social problems. It leans toward reducing taxes (though it is important to remember that the senior George H.W. Bush, in a moment of candor he regretted for a decade, once described the supply-side theology as “voodoo economics”). It believes in pre-emptive strikes against threats to American security. But it is difficult to produce a clear definition of Bushism.

Because John Kennedy was in office for so short a period – about a quarter of the time the two Bushes will have been in the White House – the emphasis on the presidential record is far less important in the case of the Kennedys than it is for the Bushes.

In the Senate, however, the younger Kennedys were clear voices for justice for minorities and the poor and strong advocates for government solutions to social problems. It is not too much to say that though Robert F. Kennedy and Edward M. Kennedy might have been drawn to politics for purely dynastic reasons, they came to see politics and government as tools for reforming America and for using government programs to attack social problems such as racism and social challenges such as health care.

Today, Americans are much less eager to use government as a blunt tool to create social change, but the fact that the Kennedy ethos is out of fashion does not make it less vivid. So while the Bush dynasty may be more robust than the Kennedy dynasty, the Bush legacy might be less sharply defined.

Kennedys’ impact endures

For I think it is fair to say that the Kennedys, while perhaps not quite as accomplished in winning office as the Bushes, might well have an impact more enduring. My rationale: The Kennedys have sown more thoughts in the minds of Americans than the Bushes.

This is difficult to prove, but apart from Mr. Bush’s statements of resolve after Sept. 11, 2001, there are few Bush thoughts that will outlive him. (An important exception is this excerpt from Mr. Bush’s commencement address at the University of Notre Dame in 2001, when he said: “I leave you with this challenge: Serve a neighbor in need, because a life of service is a life of significance. Because materialism ultimately is boring, and consumerism can build a prison of loss. Because a person who is not responsible for others is a person who is truly alone. Because there are few better ways to express our love for America than to care for other Americans. And because the same God who endows us with individual rights also calls us to social obligations.”)

But the Kennedys have left us with many such enduring thoughts. They have urged us to “ask not what your country can do for you” (John F. Kennedy). They have bidden us “to tame the savageness of man and make gentle the life of this world” (Robert F. Kennedy). They have reminded us that, in the service of others, “the work goes on, the cause endures, the hope still lives and the dreams shall never die” (Edward M. Kennedy).

This is not a soundbite derby, nor a duel between two presidents with unpopular wars (Vietnam and Iraq), nor one about poll ratings. In this question, Mr. Bush’s 38 percent job-approval ratings (Zogby poll, March 6) are completely without meaning. Harry Truman had low poll ratings, and today he is remembered as a sage.

Instead, this is a set of questions that helps us to see the accomplishments the Bushes have made and the work the Bushes have left undone. Fortunately for the president, and for us, time is not up.