WASHINGTON – When President Donald Trump tweeted "All is Well!" Tuesday after Iran's missile attack on two U.S. air bases in Iraq, the danger of imminent war seemed to have passed.

No casualties. It was a warning shot, said a U.S. official after dawn broke Wednesday in the desert. Many outside national security experts agreed, saying they believed Iran took deliberate steps to avoid American casualties. And in a televised address, Trump spoke of "minimal damage" and "Iran standing down" in a relatively restrained retaliation for the U.S. drone strike that killed Iran's second-most powerful figure, Maj. Gen. Qasem Soleimani.

But by dusk in Washington, the official assessment had darkened. Chairman of the Joint Chiefs of Staff Mark Milley became the first of several administration officials to assert Iran had indeed sought to kill U.S. soldiers and destroy vehicles and warplanes.

Days later, Iran's intentions remain a subject of intense debate and some outside experts harbor doubts about Milley's assertion. Iran has been even less clear. Brig. Gen. Amir Ali Hajizadeh, commander of Iran’s Revolutionary Guard’s Aerospace Force, said Tehran was not trying to kill anyone "although tens of US troops have likely been killed and wounded," according to Iran's Fars News Agency.

The question of whether Iran tried to kill U.S. soldiers or merely rattle Americans with a warning shot is significant because the answer hints at how far Tehran is willing to go to challenge the country it calls the "Great Satan."

Persian Gulf:Iran got its revenge for Qasem Soleimani's killing but the US Navy is still a target

"This is the first, not the final, shot from Iran," said Eric Brewer, a fellow at the Center for Strategic and International Studies who focused on Iran issues at Trump's National Security Council. "Whether or not Iran intended to kill Americans, I don't think we should expect that this is the only step that Iran is going to take on."

If Iran wanted to, it could have

In the chaos before dawn on Wednesday, officials scurried to assess damage from 16 short-range ballistic missiles that Iran had fired at two air bases U.S. and coalition troops occupy in Iraq: al-Assad in the western part of the country and Erbil in the north. Eleven missiles struck at al-Assad, and one fell near Erbil. The rest failed to reach their targets. 

By midmorning Wednesday, those officials, privy to initial assessments, told USA TODAY that the lack of casualties and relatively minor damage to tents, a helicopter and a hangar probably were intended as a warning that worse could be in store. Part of that theory rests on Iran's capability, displayed in September, to target with precision and damage oil production facilities in Saudi Arabia. If Iran wanted to hit a target, a senior U.S. official said, it would have.

That view gained currency with Trump's address. Backed by Defense Secretary Mark Esper, Vice President Mike Pence, Milley and members of the Joint Chiefs of Staff, Trump signaled Wednesday that tit-for-tat steps toward war seemed to have stopped.

"Iran appears to be standing down, which is a good thing for all parties concerned and a very good thing for the world," he said.

Trump vs. Tehran:Iraqis stuck in the middle in battle for Middle East influence

By Friday, the message had changed. Secretary of State Mike Pompeo told reporters, "There’s no doubt in my judgment, as I observed the Iranian activity in the region that night, they had the full intention of carrying – killing U.S. forces, whether that was our military folks or diplomatic folks who were in the region."

National security experts and many prominent lawmakers suggested that if Iran's aim was to kill U.S. troops, it would have launched more missiles and probably picked different targets, such as the U.S. Embassy in Baghdad or other parts of the Green Zone where there could have been hundreds of casualties, if not more.

The Iranians waged the bet, fraught with risk but deemed necessary, to launch a conventional attack on U.S. forces to avenge Soleimani's death. 

Mark Quantock, a retired two-star Army general who served as director of intelligence for Central Command, said it appeared Iran sought to mitigate the risk by signaling the strike long enough in advance to allow U.S. forces to prepare.

In fact, the attack did not surprise U.S. forces. 

Troops had hours to prepare for the attack, dispersing personnel to bunkers well before the missiles crashed down, according to a U.S. official not authorized to speak publicly. The warning came from U.S. intelligence sources and was shared with American allies, the official said.

“They were trying to kill equipment and housing,” Quantock said. “They signaled the attack and knew we were watching. Through technical means, we would know that they were fueling missiles and positioning them. They also knew the Iraqis would tell us.”

Second attack:Pentagon launched second attack on an Iranian militant the same day it killed Soleimani

Deaths would have sparked retaliation

But if what Pompeo and other officials are now asserting is true – that Iran ordered a lethal strike – the U.S. was a lot closer to war this week than many people assumed. 

Given time to shelter in bunkers, U.S. forces across Iraq withstood the attack by more than a dozen ballistic missiles. Iran’s goal was to destroy several aircraft and perhaps a munitions bunker that could generate a spectacular explosion, Quantock said.

Had any Americans died, a strike on the Iranian bases that launched the missiles almost certainly would have been the Pentagon's next move, he said.

“Now you’re hitting Iran proper,” he said. “That ups the ante substantially.”

Trump's war powers:House votes to limit President Trump's war powers after Soleimani killing

On Friday, U.S. officials reported Iraq was quiet. And it may remain so for some time, Quantock said, but it's hardly over. 

“This is phase one of their response,” he said.

Thomas Warrick, a senior fellow at the Atlantic Council, pointed to Iran's "peculiar sense of symmetry" when it comes to its international views and taking action against the U.S.  

"What we or our allies do to them, they do back to us, not exactly in the same way, but in a similar way," he said during a panel discussion Thursday. "This in fact makes Iran much more predictable than I think many people opining on these issues tries to say."

While experts agreed further military strikes from Tehran were unlikely, Warrick pointed to comments by President Hassan Rouhani and the Islamic Republic's Supreme Leader, Ayatollah Ruhollah Khomeini, who have both said Iran's strategic objective is to drive U.S. forces from the region. How Iran plans to achieve that goal is less clear. 

Trump-Trudeau:Downing of Ukrainian airliner Iran could draw Trump and Trudeau together

'Blood for blood'

Iran, as Trump noted, may be standing down. For now. Quantock said he expected two more waves of attacks in the coming weeks and months.

The next threat comes from the Iranian-backed militias whose rocket attacks killed an American contractor on Dec. 27 near Erbil. They also laid siege to the U.S Embassy in Iraq. Soleimani had firm control over their actions, but his successor is expected to have less influence. They held Soleimani in high regard and will seek vengeance.

“Blood for blood,” Quantock said. “Likely mortars or rocket attacks. Damage, explosions and casualties.”

Such proxy forces, long fostered by Soleimani, pose greater risks of renewed conflict with Iran because the Trump administration has been quicker than prior administrations to blame Tehran for attacks by regional militia groups, CSIS's Brewer said. 

Iran sanctions:Trump administration hits Iran with new economic sanctions

The most recent spate of tensions between Washington and Tehran came after Pompeo blamed Iran for attacks on Saudi oil refineries in September that disrupted 5% of the world's global oil supply. Yemen's Iranian-backed Houthi rebels claimed responsibility for the strikes, but Pompeo insisted Iran was behind the attacks. Trump responded by imposing harsher sanctions on the Islamic Republic. 

Finally, the Quds Force that Soleimani led has international reach, creating risks for U.S. embassies and personnel around the world.

Still Warrick warned the gamble the Iranians took show they're relying too much on luck, noting it was "by the grace of God no one was killed" during the strikes on the two Iraqi air bases. 

"It's a huge mistake to rely on luck to save your country from a major and devastating military response, which would have been the case if someone simply decided to go out and retrieve an item in their tent," he said.

"And that kind of action is as dangerous as anything else that I've heard criticized from any party in this dispute," Warrick said. 

Ilhan Omar:Republicans mock Ilhan Omar for saying Iran war talk sparked PTSD