Midway into the fourth week of the Iran war, the United States has been pursuing three alternative endings simultaneously: a diplomatic path, a continuation and intensification of the air campaign, and preparations to reopen the shipping route through the Strait of Hormuz by force.

Although the facts on the ground are always shifting, none of these scenarios seem likely to bring a quick end to the war. The longer the war lasts, the greater the likelihood that ground troops will be needed. I believe this also raises the possibility of Russia and China increasing their support for Iran's efforts.

These alternatives are more clearly discerned today than they were at the end of the second week of the war. No end to the conflict is in sight, but the primary issues have come into focus much more sharply.

US, Israeli strikes didn't destroy Iran's capability to respond

After 25 days, U.S. and Israeli air strikes have wreaked incredible destruction in Iran, largely against military and regime targets, but Iran still maintains a distributed Islamic Revolutionary Guard Corps (IRGC) chain of command and can still launch drones or ballistic missiles against Israel and friendly states in the Persian Gulf.

There is no sign yet of Iranian forces collapsing or a large uprising against the regime. Gulf states are significantly impacted militarily and economically by Iranian strikes, and most would like the conflict to end immediately. Meanwhile, most European states have refused to join the conflict.

The major emerging issue is Iran’s closure of the Strait of Hormuz: The impact on oil, fertilizer and helium transported through the strait – all critical commodities and comprising 25% to 30% of global supply – threatens massive economic dislocation in energy, agriculture and computer chip manufacturing.

At home, there is criticism of the war (partisan, of course), but also criticism of the apparent failure to protect regional allies and keep the strait open. Such criticism, warranted or not, encourages Iran to keep up its resistance.

On March 23, President Donald Trump announced progress in ongoing talks with the Iranian government, while Iran said no talks were underway. By the next day, it was apparent that talks were underway, but faced significant challenges.

The Iranian government is likely split, with some political leaders seeking an end to the conflict and IRGC commanders resisting, because they believe they are winning. Who are we talking to, and do they have the authority to deliver on any agreement?

Then, what are the conditions that could be part of an agreement? Will Iran surrender its enriched nuclear materials, dismantle its enormous missile and drone production, and open the strait to all traffic?

Will the United States and Israel agree never again to attack, and allow Iran to enrich uranium for peaceful purposes? How will freedom of navigation in the Persian Gulf and through the Strait of Hormuz be assured?

Both sides seem confident of their positions

Neither side as yet appears willing to concede their aims: President Trump is still calling for Iran to surrender its enriched uranium and open the strait. Iran, having established the power of its control of the strait, will demand reparations and an end to sanctions.

This diplomacy is taking place under the threat of President Trump’s five-day timeline before he orders attacks on Iran’s energy infrastructure.

Meanwhile, the air campaign continues to strike targets, including many suspected locations on the Iranian shore of the Gulf that may store small attack boats, mines and missiles.

Despite air superiority, Israel and the United States have not yet been able to destroy all missile and drone sites, nor prevent asymmetric attacks on Israel and the regional states. It is in the nature of diplomacy in wartime that neither side will relent in its attacks until agreement is reached, and indeed, may escalate its efforts to gain advantage.

It may be tempting to believe that continuing the air strikes will eventually topple the regime, but Iran must also be encouraged by the success of its closure of the strait and its ability to continue to attack across the Persian Gulf. While the air campaign has demonstrated a remarkable ability to generate targets in the thousands, Iran has also had years to prepare for attack from the skies.

This will prolong the campaign, and while Iranian capabilities to respond are diminished, that alone is unlikely to end the conflict.

For Iran, resistance may continue for weeks and, with minimal outside support, could continue for many months. The country has shown a strong ability to innovate, with missiles that can range about 1,800 miles and warheads that maneuver and dodge Patriot missiles.

Opposing sides have different objectives

Iran understands that to win, it has only to survive ‒ while the United States buckles under global pressure to reopen the strait and under domestic pressure from an impatient U.S. electorate. Iranian resistance is based not only on the political and economic pressures weighing on America and Israel, but also on its leaders' deeply entrenched zealotry.

In the 1999 air campaign against Serbia, NATO could count on Serbian President Slobodan Milosevic’s ultimate rationality. It took 11 weeks, but he ultimately gave in to the escalating air attacks and the threat of ground troops.

We should not expect IRGC commanders to be as susceptible to this kind of pressure. They could well decide, irrationally, to resist far longer, as Hamas has in Gaza.

If so, this will lead to an amphibious and airborne operation to open the strait. Initial discussions have centered on Kharg Island, the key Iranian export hub. Its seizure would substantially halt Iran's oil exports. That would be a bargaining chip, but would not assure that the strait would be reopened.

For that, a much larger operation likely would be necessary, entailing seizure of multiple islands in the strait and probably dealing with mines, missiles, drones, torpedoes, cruise missiles and other threats from the shoreline.

Protecting shipping means controlling this whole shoreline, its people and the airspace above it.

Major U.S. troop deployments are now underway – two Marine Expeditionary Units, special forces and perhaps a large portion of the 82nd Airborne Division – but preparation even to commence action will probably take another week or so. And, in what could be called “a rolling start,” deployment could then be continually reinforced by the introduction of more troops.

The best outcome is an immediate ceasefire and reopening of the Strait of Hormuz. Iran’s nuclear and missile programs have been steeply degraded, but Iran has an extraordinary capacity to absorb punishment. As long as Iran believes it is winning, the end may be many weeks away.

Wesley Clark is a retired U.S. Army general and former NATO Supreme Allied commander in Europe.

© USA TODAY