It is the sort of moment when peace and history could be hanging in the balance for a generation to come—the kind of tipping point when American presidents can no longer leave the negotiating to underlings. They must take the world stage themselves to find a new way out, simply because no one else has the globo-oomph to do so. There is a grand American tradition behind this sort of personal involvement of America’s chief executive, one that goes back almost precisely a century. Teddy Roosevelt spent much of August 1905 directing talks in Portsmouth, N.H, that prodded Japan and Russia into an agreement ending the Russo-Japanese war. Woodrow Wilson went to Paris for nearly six months between January and June of 1919 to negotiate the end of World War I. Franklin Roosevelt, though he was dying and suffered a terrible physical disability, flew halfway around the world to hash out the postwar peace at Yalta. Richard Nixon went to China, Ronald Reagan journeyed to Reykjavik and Jimmy Carter holed up at Camp David, where he tested the limits of brinksmanship with Menachem Begin and Anwar Sadat.

George W. Bush is going to Kennebunkport, where he’ll test his golf skills with Poppy.

Maybe that’s an unfair slap. After all, Bush’s father also went to the family compound at Kennebunkport in the early stages of the Persian Gulf crisis in August 1990, and he ably managed that affair in the end. But the son’s disengagement is of a more profound kind than mere place. Bush’s approach to personal involvement in international affairs today is pretty much still what it was on inauguration day, Jan. 20, 2001. He doesn’t want to be Bill Clinton, who gave presidential diplomacy a bad name with his frenzied (and often failed) efforts to cut various peace deals in his final months. Bush’s instinct is to give the world its operating instructions—as he did again at his news conference on Monday—to reiterate his strategic goal of delivering freedom to the unfree, and then head off for some exercise.

Events, sadly, have rendered that approach inadequate. With matters flying out of control, the president can no longer merely hold occasional news conferences and utter his simple, already hoary formula that all terrorists are the same and that they all want to halt the advance of liberty. Not at a time when it’s clear to everybody that the advance of liberty, messy as it is, has actually empowered Islamist parties in Iraq, in Lebanon and in the Palestinian territories, and when Hezbollah and Iran want something quite different from Al Qaeda. Even Bush’s domestic audience—to which he mainly directs his comments—no longer buys the absurdly one-dimensional notion that all terrorists are the same, according to a new CBS News/New York Times poll that shows a majority of Americans now separate what’s happening in Iraq from the war on terror.

Nor can Bush merely rely on making the occasional phone call, as he did to Chinese President Hu Jintao on Monday over the North Korea problem. The crisis in the Middle East and Iran, especially, have reached such a level of complexity that only sustained intervention by the United States at the highest level can make a difference. Consider Lebanon. Left unaddressed in the recent U.N. ceasefire resolution was the critical issue of border control of weapons flows to Hizbullah from the northeast, in other words Syria (the resolution deals only with the southern border). Now Israeli officials—who are still in a state of shock over the sophistication of Hizbullah’s weaponry—are expressing anger that countries like China, which sold Silkworm missiles to Iran, and Turkey, which shares a border with Iran, have allegedly permitted Tehran to send these weapons on to the militant group. Russia, meanwhile, refuses to end shipments to Syria of antitank missiles that, Israel charges, ended up shredding Israeli tanks. Only Washington possesses the alliance network and prestige to resolve a multidimensional problem like this.

And maybe only Washington can offer the kind of guarantees that the Europeans seek to prevent their peacekeepers from getting caught in the Lebanon cross-fire. The delays in putting up troops, especially by France, are not just a matter of European flip-flopping. They reflect legitimate concerns over murky rules of engagement. The French military, especially, has warned President Jacques Chirac that the Lebanon peacekeeping deployment could turn into another UNProFor, the ill-starred U.N. force that had nightmarish encounters with brutish Serb militias in Bosnia in the ’90s. “They were asking Chirac to recall what happens to a multinational force with a very complex command, weak mandate and complicated execution,” a senior European official told me.

Who has the ability to reassure the French president on this score? Only another president—an American one.

When it comes to Iran’s nuclear program, the U.S. approach is still to push ahead to economic sanctions, beginning with an expected U.N. Security Council resolution on Aug. 31. But it’s obvious that these slow-moving Western pressure tactics—with Germany, France and Britain taking the lead while Washington backs them up—have already failed. Iran needs only six months or so, assuming it overcomes its current technical difficulties, to master the nuclear fuel cycle. Tehran is gambling that its ambiguous response Aug. 22 to a Western package of incentives will be just enough to keep China and Russia from backing tougher sanctions in the Security Council. And that’s the whole ballgame. Even if the U.S.-European effort does manage to get Beijing and Moscow to sign onto harsh Chapter 7 sanctions, it’s clear Tehran can withstand them long enough to gain the nuclear knowhow it needs. Barring an airstrike, absolutely nothing is going to stop this except a brand new deal of the diplomatic deck.

Even that, of course, may not work. Iran is in as powerful position as it has been in its modern history, and its current president, Mahmoud Ahmadinejad, is a fanatic (unlike his pragmatic predecessor, Mohammad Khatami, who now wants to travel to Washington). But something new must be tried, and Tehran has sent out numerous signals in recent months that it wants to deal mainly with Washington. America is the only power that can offer the kind of security guarantees that might, even at this late stage, prompt Iran to stand down from its nuclear weapons program. The only alternative is military action, which may well come from Israel. And that could open a Pandora’s box of new troubles that might even make the Iraq quagmire look mild.

The world faces more than a security vacuum. What we are suffering is a vacuum of global leadership. That is why the “international community”—always a tenuous concept at best—seems to be coming apart at the seams, why China and Russia are going their own way, why the Europeans are clucking around like headless chickens, why the moderates in the Mideast have fallen silent. Bush must recognize that the world is not following his lead, if it ever did, and that he needs to change his tack. He needs to jump in with both feet.

Despite his “stay the course” reputation, this president has shown he can adapt. For the first year or so of his second term there was a sense that Bush understood how much his first-term unilateralism had cost him. Still, even as he eagerly joined multilateral talks on Iran and North Korea, he remained determinedly disengaged on a personal level. His attitude was: let China take the lead (Korea); let the “EU-3” take the lead (Iran).

Now Bush has a little over two more years left to take the lead himself, to recognize his place in a long U.S. tradition of American presidents who have understood that their global responsibility is to solve the knottiest international problems no one else can master. But to do so Bush must change his whole approach. As he heads off to Kennebunkport, there’s reason to doubt that he will.