Donald Trump has pushed a tough line on Iran, and some close advisors have pressed the US president to get even tougher.
He has abandoned an international nuclear agreement, slapped sanctions on Iran and added its Revolutionary Guards to a terrorist blacklist.
Tensions have skyrocketed following Iran's shooting down of an American surveillance drone Thursday.
With the Pentagon lacking a permanent boss since December's shock resignation of James Mattis, hawkish aides and legislators may hold even more sway over the president, long an opponent of "endless" American wars.
These are the main players:
- John Bolton -
Trump's national security advisor is his chief saber-rattler, a champion of regime change in Cuba, Iraq, North Korea, Venezuela and now Iran.
Bolton issued a stern warning to Tehran in 2018, saying "we will come after you" if the country does not curb its aggression, and Iran's Foreign Ministry has branded him a "warmonger."
Bolton has praised Trump's "fantastic" decision to exit the nuclear deal, and experts believe he has advocated bombing Iran for years.
The 70-year-old said Iran was "almost certainly" behind May 12 attacks on four ships off the United Arab Emirates, and he has focused so completely on neutralizing the Iran threat that Trump himself has sought to rein him in.
"I actually temper John which is pretty amazing," Trump acknowledged last month.
- Mike Pompeo -
Trump's second secretary of state assumed his post in early May 2018. One week later, the president withdrew the United States from the nuclear deal and re-imposed harsh sanctions on Iran.
While Pompeo recently has sought to hew to Trump's more restrained line, insisting Trump "does not want war," the top US diplomat is seen as advocating aggressive policies to counter and further isolate Iran.
As a congressman, Pompeo in 2004 urged Washington and allies to consider launching strikes "to destroy the Iranian nuclear capacity," ABC News reported.
In May, the State Department ordered non-emergency staff evacuated from its Baghdad embassy due to an "imminent" threat from Iranian-linked militias. Shortly thereafter Pompeo said the administration was bypassing Congress to sell weapons to Saudi Arabia in order to "deter Iranian aggression."
After the US announced it was sending another 1,000 troops to the region, Pompeo said this week that he was eager to "achieve the strategic objectives" set forth by Trump.
"But we can't do that without making sure we have the capability to respond if Iran makes a bad decision" like attacking American interests.
- Lindsey Graham -
Few lawmakers have had the impact on Trump's foreign policy as Graham, a US Air Force veteran who consistently advocates an interventionist approach.
The senator from South Carolina has spoken of strict "red lines" for Iran, and hinted at one Wednesday by telling Fox News that the United States should "take out their navy, bomb their refineries" if Iran further disrupts shipping in the Strait of Hormuz.
On Thursday he offered eye-popping comments on the Iran threat. Iran's leaders should brace for "severe pain inside their country," Graham told reporters as he ticked off several "provocations" including attacking Japanese vessels and shooting down the US drone.
As for Trump, "he's trying to avoid conflict, but this is truly a defining moment for him," Graham said.
"If you are not willing to take this enemy on, you will regret it."