WASHINGTON (AFP) - United States President Donald Trump has pushed a tough line on Iran, and some close advisers have pressed the 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 on Thursday.
With the Pentagon lacking a permanent boss since December's shock resignation of Mr 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:
Mr Trump's national security adviser is his chief sabre-rattler, a champion of regime change in Cuba, Iraq, North Korea, Venezuela and now Iran.
Mr Bolton issued a stern warning to Teheran 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".
Mr Bolton has praised Mr 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 neutralising the Iran threat that Trump himself has sought to rein him in.
"I actually temper John which is pretty amazing," Mr Trump acknowledged last month.
Mr 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 Mr Pompeo recently sought to hew to Mr Trump's more restrained line, insisting Mr Trump "does not want war", the top US diplomat is seen as advocating aggressive policies to counter and further isolate Iran.
As a congressman, Mr 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 to evacuate from its Baghdad embassy due to an "imminent" threat from Iranian-linked militias. Shortly thereafter, Mr 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, Mr Pompeo said this week that he was eager to "achieve the strategic objectives" set forth by Mr 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.
Few lawmakers have had as much impact on Mr Trump's foreign policy as Mr 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 on Wednesday by telling Fox News that the US 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", Mr Graham told reporters as he ticked off several "provocations" including attacking Japanese vessels and shooting down the US drone.
As for Mr Trump, "he's trying to avoid conflict, but this is truly a defining moment for him," Mr Graham said.
"If you are not willing to take this enemy on, you will regret it."