When American and Israeli warplanes struck Iran on February 28, 2026, killing Supreme Leader Ali Khamenei in the opening hours of the campaign, Washington framed the operation as an urgent act of nuclear non-proliferation.

The objective appeared straightforward: prevent Iran from becoming a nuclear weapons state.

Five months later, that justification has largely disappeared.

Instead, the conflict has evolved through successive phases — from a campaign against Iran’s nuclear programme to a military effort to reopen the Strait of Hormuz — and is now increasingly about preserving American credibility after both objectives proved more elusive than expected.

When the mission shifted

Iran’s response changed the character of the war almost immediately.

Rather than escalating solely through missile exchanges, Tehran closed the Strait of Hormuz, allowing only approved vessels to pass while targeting ships that ignored its restrictions.

Overnight, the conflict ceased to revolve primarily around uranium enrichment.

It became a struggle over one of the world’s most strategically important waterways.

By March, Washington’s military priorities had shifted accordingly.

US Central Command launched operations aimed at reopening the strait, while in April it imposed a naval blockade on Iranian ports.

President Donald Trump appealed to NATO and China to help secure maritime traffic. Neither agreed.

Perhaps the most revealing moment came when Trump remarked that the United States “did not need the oil” flowing through Hormuz.

Whether rhetorical or not, the comment acknowledged what events had already demonstrated: Washington was no longer fighting primarily over centrifuges.

The credibility deficit

Today, Washington’s stated objective has shifted again.

With the June ceasefire already under strain and Iran continuing to attack commercial vessels outside its designated shipping corridor, Washington now threatens to destroy Iranian infrastructure for every merchant ship targeted.

International law experts have warned that publicly threatening retaliation against civilian infrastructure would raise serious legal concerns.

Secretary of State Marco Rubio’s remarks in Manila this week reinforced the evolution in Washington’s narrative.

His warning that no country should be allowed to charge tolls or attack shipping in international waters was less about nuclear proliferation than about preserving a long-standing principle: freedom of navigation.

That principle matters enormously.

Yet it also exposes an uncomfortable reality.

The world’s pre-eminent naval power has struggled to guarantee free navigation through a waterway it has long promised to keep open.

That failure may prove more consequential than any battlefield outcome.

For decades, the Gulf’s security architecture rested on a simple bargain.

The United States maintained overwhelming military superiority, while Gulf monarchies offered strategic access and energy cooperation in return for protection against regional threats, particularly Iran.

The war has exposed the limits of that arrangement.

According to Al Jazeera, Iranian missile and drone attacks have struck every Gulf Cooperation Council state despite none of them directly participating in the initial offensive.

Whether or not those attacks caused strategic damage, they undermined the central assumption underpinning the American security umbrella: that Washington could deter retaliation against its partners.

The Gulf recalculates

Regional capitals have taken notice.

CNN reports that Saudi Arabia and Qatar are considering a broader non-aggression framework with Tehran while increasingly envisioning a Gulf security order in which the United States plays a less dominant role.

As Simon Mabon, professor of international relations at Lancaster University, told Al Jazeera, the conflict has “pierced” Gulf confidence in American protection, describing Washington’s security umbrella as “moribund at worst, or ineffective at best.”

That assessment may sound harsh, but it reflects a growing strategic dilemma.

No Gulf state appears ready to abandon its relationship with Washington.

Yet none can ignore the vulnerabilities the conflict has exposed.

China possesses economic influence but has shown little appetite for assuming the military responsibilities the United States has carried for decades.

The Gulf states therefore face an uncomfortable reality: they cannot fully trust the existing security guarantee, but neither can they replace it.

Beyond the nuclear question

Seen in that light, Washington’s changing rhetoric becomes easier to understand.

The emphasis on defending freedom of navigation is no longer simply about keeping trade routes open.

It is also about preserving the credibility of an American-led regional order that now looks considerably less certain than it did before February.

Rubio’s insistence that Gulf leaders harbour no doubts about US security commitments sounded less like reassurance than recognition that those doubts now exist.

Iran’s nuclear programme has not disappeared. It remains damaged but intact, and it will almost certainly return to the centre of regional diplomacy.

For now, however, the defining issue is no longer centrifuges.

It is whether the United States can still deliver the security guarantees that have anchored Gulf politics for half a century, or whether this war will ultimately be remembered as the moment when the region began preparing for a post-American security order.

That is a far more consequential question than the one Washington set out to answer on February 28.