Originally Published: 01 AUG 22 22:17 ET

Updated: 02 AUG 22 07:57 ET

Analysis by Stephen Collinson, CNN

(CNN) -- For a few hours, America's first war of the 21st century -- the war on terror -- returned to supersede the stirrings of a geopolitical showdown set to dominate the coming decades: a super power face-off with China.

In a blast from a previous foreign policy era, the US announced Monday that it had killed al Qaeda leader Ayman al-Zawahiri in a drone strike in Afghanistan, settling one of the last outstanding debts of vengeance after the September 11, 2001 attacks.

The killing was seized upon by President Joe Biden as validation of his vow to prevent the war-torn South Asian country from again becoming a safe haven for terrorists, despite ending America's longest war there last year. And it may offer a steadying moment as the anniversary of his disastrous Afghanistan withdrawal nears, adding to his presidency's momentum after Senate Democrats struck a deal on a climate, energy and health care bill last week.

More broadly, the attack, which hearkens back to the war on terror but coincides with a moment of soaring US tensions with Beijing, underscores a profound pivot in US national security policy.

At one time, finding terrorists who attacked America wherever they were hiding was the organizing principle of Washington's approach to the world. While Monday's news was a "mission accomplished" moment, simmering tensions over Taiwan show how the US government is now building a new national security machine to challenge China's rising power.

A significant moment

There is deep symbolism in the killing of Zawahiri, an Egyptian surgeon turned radical Islamic ideologue who was wanted by the US for years even before the 2001 attacks on New York and Washington.

Zawahiri was indicted by the FBI for his alleged role in the bombing of US embassies in Kenya and Tanzania in 1998, which heralded a new age of al Qaeda terrorism directed against Americans. He had a key role in the bombing of the USS Cole in Yemen in 2000. Successive presidents vowed to bring the leaders of bin Laden's terrorist network to justice, and Biden is the latest to have done so, in one of the few common threads in recent US foreign policy spanning administrations.

"Now justice has been done. This terrorist leader is no more," the President said, addressing the nation from his Covid-19 isolation on a balcony overlooking the South lawn of the White House on Monday evening.

If Zawahiri lacked the charisma and mobilizing power of bin Laden, killed in a daring US Navy SEAL raid in Pakistan in 2011, his influence and organization of al Qaeda resulted in huge damage to the US. His demise validates American vows to pursue its enemies to the end of the earth.

"In many ways, it bookends the operation to go after bin Laden," former CIA Director and Defense Secretary Leon Panetta told CNN's Erin Burnett on Monday.

He added that the loss of Zawahiri means al Qaeda no longer has the leadership structure to pose a threat to the United States or its allies.

A bonus for a wobbling presidency

More immediately, the death of Zawahiri represents a significant moment for Biden and his wobbling presidency.

It may go some way to purge painful memories of the chaotic US withdrawal from Afghanistan a year ago. It may help the administration recast what are likely to be damning anniversary reviews of that foreign policy failure later this month. And more importantly, the strike backs up Biden's claim to be able to target US enemies in Afghanistan from "over the horizon" -- part of his argument that America no longer needs to maintain large land armies on foreign battlefields.

While Zawahiri was unable to reconstitute al Qaeda after the death of bin Laden to its former power, the circumstances of his death stand as a warning to other terrorist groups in Afghanistan and elsewhere. However, the fact that Zawahiri was apparently killed in an attack on a house in the center of Kabul raises real concerns that Afghanistan -- back under Taliban control -- is yet again harboring al Qaeda.

But it also shows that the US has intelligence capabilities in Afghanistan despite the exit of US diplomats, military and intelligence officials from the country last year. Biden chose the more optimistic takeaway, arguing that the operation proved his promise that he would not allow Afghanistan to again become a safe haven for terrorists.

Presidents typically don't take life-and-death decisions about national security to massage their own approval ratings -- at least most of them don't. But they all operate in a political context because of their position. There is no doubt that Biden could benefit incrementally from his commander-in-chief moment on television, reporting from the White House to Americans about the killing of an enemy.

The drone strike in Kabul came as Biden was being assailed by Republicans as weak and incapable. During the US departure from Afghanistan, Biden's reputation as a safe pair of hands on foreign policy took a hit as Americans watched scenes of desperate refugees falling to their deaths from departing US planes, and the US military admitted to a botched drone strike that killed 10 Afghan civilians -- including seven children.

But it's also unlikely that Monday's news will do much to alter the fate of Democrats in November's midterm elections, who fear heavy losses amid new signs the economy could plunge into recession and following months of punishing high inflation. Foreign policy victories can be fleeting, and decapitating terror groups no longer brings the political payoff that it did when then-President George W. Bush was keeping score in the years after 9/11.

It may take a few days to fully assess how Zawahiri was located and to confirm the White House versions of events. On occasion, administrations have gotten details wrong or out of context in early readouts. Biden's assurance that no civilians were killed in the drone strike could not immediately be confirmed.

In an increasingly polarized nation, the killing could offer a rare moment of unity -- even if the distance from the 9/11 attacks and the relatively low profile of Zawahiri didn't send crowds to chant outside the White House as was the case when bin Laden was killed.

Still, any satisfaction over the killing of Zawahiri is likely to be soon overtaken by a more multilayered and urgent US conundrum abroad -- the possibility of a standoff over Taiwan that threatens to erupt even as the US wages an effective proxy war against Russia in Ukraine.

US and Taiwanese officials have said that House Speaker Nancy Pelosi is expected to defy increasingly irate warnings in Beijing and fly into Taipei. Some foreign policy experts fear the trip could provoke an unprecedented Chinese response.

Presidents know only too well that when one national security threat is extinguished, the next is just over the horizon.