The four-star Marine commander, who served as CENTCOM’s top strategist and then Marine chief in the region in the early days of the US-led fight against the Islamic State in Iraq and Syria, will likely have to contend with growing tensions with Iran without legal authorities from Congress or clear guidance from the president on the military front.

But the back-and-forth over the carrier deployment — which was routinely announced by the US Navy in April before national security adviser John Bolton put it in the public spotlight with a statement on Sunday — demonstrates the challenge McKenzie will face in his new job.

Gen. Frank McKenzie, the newly tapped US Central Command chief who pushed to speed up the carrier group's deployment, said the move “sends a clear and unmistakable message” at a conference of the hawkish Foundation for Defense of Democracies in Washington. “Iran should not confuse our deliberate approach with an unwillingness to act.”

US Central Command said today that the USS Abraham Lincoln had arrived in the Middle East along with four bombers.

Days after the Donald Trump administration touted the deployment of an aircraft carrier group and a suite of radar-busting bombers to the Middle East as a warning to Iran, the Pentagon’s new top commander in the region used his first public appearance on Wednesday to pin the country as the region's greatest long-term threat to the United States.

“Ultimately this is Trump’s decision, and he has not weighed in directly on this issue,” said Andrew Miller, a former Barack Obama administration official. “It just may be that this is sort of a Venn diagram where coming from two different perspectives, CENTCOM and Bolton have agreed on the same deployment.”

CNN reported on Tuesday that US intelligence on Iranian ship movements of short- and medium-range ballistic missiles had prompted the decision to respond with the carrier deployment. During the Trump administration, the United States has not consistently kept an aircraft carrier in the region.

Sending a group of B-52 bombers to the region is designed to stop the Iranians from contemplating an attack on US forces or allies in the region, former US officials told Al-Monitor, as the administration has escalated its so-called “maximum pressure” campaign on Iran.

“At the end of the day, it’s really designed to make sure that the Iranians don’t do anything foolish on an asymmetric basis. There’s a lot of things that they can do based on the nature of their forces where it’s not a direct affront to the US,” said John Miller, a US Navy vice admiral who led American vessels in the Middle East before retiring in 2015. “The moves that we’ve made militarily are designed to say, ‘don’t do that,’ because then we’re prepared to respond along with our friends and allies in the Gulf.”

But a US response from the air would require the permission of Qatar, which has been blockaded by several Gulf countries led by Saudi Arabia since June 2017 over its relationship with Tehran and the Muslim Brotherhood. The country’s Al-Udeid air base is the only US runway in the region long enough to allow the bombers to take off.

Some members of Congress insist that the Trump administration would need permission to go after Iran militarily. “Let me make one thing clear: The Trump administration has no legal authority to start a war against Iran without the consent of Congress,” said Sen. Tim Kaine, D-Va., who has pushed back against past legal justifications for military action from both the Trump and the Obama administrations.

The Pentagon has recently emphasized its ability to switch the flow of forces into the Middle East on and off as it has removed more permanent assets in the region. Last month, the Defense Department rapidly shifted a high-tech air defense battery to Israel in an effort to offset Iran’s scud and ballistic missile strength. “This is really a good example of dynamic force employment,” said Becca Wasser, a researcher at the RAND Corporation.

But even as his administration has stepped up the pressure on Iran with renewed sanctions targeting its metals industry, Trump himself indicated a willingness to cut a deal with the Iranian regime on Thursday. “I'd like them to call me,” he said.

Even with the week of intelligence warnings permeating the headlines, experts say that if the Iranians do hit the United States, it’s likely to come as a surprise.

“It’s likely to be something asymmetric that’s hard for us to discern and pin on the Iranians right from the get-go,” said Miller, the former naval commander. “That’s the way they tend to operate. It’ll likely be a response that will surprise us in a way that we’ve not quite thought through or we’re not able to see through right now.”

On Thursday, Trump moved a step closer to filling the Pentagon’s top job, announcing that the White House intends to nominate Acting Defense Secretary Patrick Shanahan for the permanent post.