For all these weeks and months, we have looked at George W. Bush through the lens of a microscope, which shows us a president’s scar tissues, exaggerates his flaws and attributes, enlarges the small characteristics that otherwise escape the eye. It might be healthy, about four weeks from the election, to look at the president through a telescope, which tells us what stands out about a political figure from afar.

For through the telescope a remarkable thing becomes clear: While so many of his 20th-century predecessors can easily be described as transitional presidents — a phrase that, because it has the tendency to diminish a president’s importance in history, was a special irritant to Bush’s father — it is apparent that Bush may not be a transitional president at all. There are many reasons to think that Bush will stand out in history for having forged a dramatic departure in the presidency.

Through the microscope — and in our memory — the presidents of the past half-century have been distinct individuals: One is remembered for his golf and, by revisionists, his guile (Eisenhower), and another for his rhetoric and vision (Kennedy); one for the splendor of his domestic dreams and for the sadness of his foreign-policy tragedy (Johnson); one for the brilliance of his mind and the commonness of his character (Nixon); another for his good-hearted effort to bring good and heart back to the White House (Ford). Still others are remembered for idealism and inflation (Carter), for clarity and common sense (Reagan), for deftness and prudence (the first President Bush) and for cleverness and charm (Clinton).

But speed ahead a half-century or more, and the great-grandchildren of George W. Bush and Sen. John F. Kerry may regard the presidents of our time the way we look at the presidents of the late 19th century, as a long gray line of men who fade into each other in their minds and in their textbooks, no more distinct to them than Chester A. Arthur and Grover Cleveland are to us.

Indeed, regarded that way — through the telescope — the presidents of the postwar era responded to crises and viewed the world and America’s role in it much the same way their successors did.

George W. Bush is different. And the proof of it is that both his supporters, who heartily endorse the Bush departure, and Kerry’s supporters, who deplore it, agree that Bush has a worldview far different from that of any of his predecessors.

Through the telescope, all the postwar presidents faced the same challenge: the containment of menacing nation-states. Their administrations were about struggles over whether and when to project force against the threats posed by the dictatorial and the demented.

Bush sees the world differently, not as a struggle among nations but as a competition among civilizations. Other presidents — Kennedy and Reagan especially, who in history will look more and more alike, and whose rhetoric about paying any price to defeat an evil empire will merge into a giant continuum — wanted to preserve the world order, not to transform it. They were constrained by the reluctance, not the willingness, to court confrontation.

Not Bush. The 43rd president has taken the Kennedy and Reagan rhetoric seriously, and in so doing has taken it to a different level. Reagan and Kennedy — I expect a deluge of despairing e-mails from the admirers of both men for saying this — tried to stir American passions for limited goals. Bush uses those passions not only as a rallying call but also as a call for action.

This helps explain why some Reaganites — some voices within the National Review crowd, for example, and some elements of the libertarian Cato Institute, and of course the redoubtable Patrick J. Buchanan — are so skittish about Bush’s war. Reagan and Kennedy believed America should be in the world but not necessarily dominate the world. Their rhetoric — Kennedy’s “watchmen on the walls of world freedom,” Reagan’s “Mr. Gorbachev, tear down this wall” — aside, they wanted a balance of power that preserved American values more than an American hegemony that spread American values.

This is a different time, with a different challenge. And Bush has a different view. By favoring pre-emptive intervention and the notion that America represents a universal culture, Bush is suggesting that the American mission is to be missionaries for that culture. The result is what the Oxford and Harvard historian Niall Ferguson calls a “faith-based foreign policy.” In this as in so much else, Bush resembles William McKinley at the end of the 19th century more than any president at the end of the 20th century.

Kennedy and Reagan expressed some of these views, to be sure. But they didn’t implement them. Their central aim was to protect the West from expansive Soviet communism, and their motivation came from the conviction, accurate as it turned out, that Soviet communism was evil as well as dangerous. There was a worldwide struggle to win, but not a world to win.

How fundamentally has Bush changed the American calculus? This much: In the Sept. 30 presidential debate on foreign policy, the Democratic nominee affirmed that a president has the right to undertake a pre-emptive strike — a view that is at odds with many of his colleagues on Capitol Hill, especially that guardian of congressional prerogatives, Sen. Robert C. Byrd, the West Virginia Democrat. He spoke, too, of “doing what we need to do with respect to — the elections” in Iraq.

We can debate who won either of the first two presidential debates, a question suited to the political microscope. On the bigger debate — the one our grandchildren’s grandchildren will see with their telescopes — Bush is already the winner, whether or not he’s re-elected next month.