The Diplomat Season 5 Theories, Ranked by the Evidence

The theory: Hal Wyler (Rufus Sewell) uses his statement to break with President Grace Penn (Allison Janney) in public.

After Kate Wyler (Keri Russell) resigns at the G7, Hal stands and sits again when Grace tells him to "sit down". When he later joins Kate and the others who walked out, she says nothing to him and tells the press the vice president has something to say. The season ends before we hear what he says.

For this to come true, Hal has to use that microphone to reject Grace's threat to fire on countries that interfere. Against it, Hal backs Grace for most of the finale: he tells Kate she won't be speaking at the summit, presses the British prime minister with a threat of military action and brushes off pleas to tell Russia its Poseidon weapon is gone. Still, "I don't think you get to walk out and then walk back in again," Sewell told The Hollywood Reporter.

The theory: Russia finds out the US has its Poseidon, and Moscow's response drives Season 5.

The Poseidon is a nuclear-powered weapon that was aboard a lost Russian submarine off England's north-east coast, until Grace Penn (Allison Janney) and Hal Wyler (Rufus Sewell) secretly sent a US submarine to take it. In Season 4, Russia asks to retrieve its dead from the submarine, and Prime Minister Bethan Vaughn (Jodie Whittaker) lets Russian vessels into British waters, where they could discover the weapon is gone. At the G7, Grace admits the US took the Poseidon in front of the other leaders.

For that to happen, the secret has to reach Moscow, through the recovery or Grace's admission. Vaughn says Britain will honour its agreement with Russia, which keeps the recovery alive. Against it, US warships are already deployed, and Grace says the US will block Russian warships and surveillance vessels from entering European seas, which could stop the recovery.

The theory: Kate Wyler (Keri Russell) and Hal Wyler (Rufus Sewell) team up against the White House, with Kate outside government.

At the G7, Kate resigns as ambassador after kissing Hal and telling him she loves him. When he joins her outside, she is relieved, and she tells the press he has something to say.

The theory needs Kate to get a new base, and the obvious one is Washington, where Hal is based and where Stuart Hayford (Ato Essandoh), her former deputy, has just been recalled. Against it, the marriage is still raw. Earlier in the finale, Hal accuses Kate of using their reconciliation to soften a political blow she knew was coming, and without a post, her influence would run through him.

The theory: pressure builds to push President Grace Penn (Allison Janney) aside, either under the 25th Amendment or through politics.

Before surgery, the wounded Grace hands her powers to Vice President Hal Wyler (Rufus Sewell), much as Section 3 of the 25th Amendment allows. Later, Stuart Hayford (Ato Essandoh) tells Billie Appiah (Nana Mensah) that Grace, he believes, is unfit to be president. Over dinner, when Kate tells her she has behaved differently since the shooting, Grace says: "We need to face the idea that maybe I'm ... off."

Section 4 is about a president being unable to do the job, not about bad policy: the vice president and a majority of the executive departments' principal officers must declare that in writing, and the vice president then becomes Acting President without the president being removed. If the president contests it and they maintain the declaration, Congress decides, and continuing the transfer requires a two-thirds vote in each house. Section 4 had never been used as of a 2024 Congressional Research Service report. Against the theory, Grace's aggression looks like a long pattern, not a new inability: she conceived the attack on the British warship HMS Courageous long before anyone shot her.

The theory: the dissent cable written by Stuart Hayford (Ato Essandoh) comes back to haunt President Grace Penn (Allison Janney).

In the finale, Stuart, the deputy chief of mission at the US embassy in London, sends the State Department's official dissent channel a cable objecting to the warship plan. Having agreed with the cable, Secretary of State Miguel Ganon (Miguel Sandoval) takes it to Grace, and she recalls Stuart to Washington anyway.

In real life, the State Department's Dissent Channel was created in 1971, and its rules say: "Freedom from reprisal for Dissent Channel users is strictly enforced." For the theory to come true, someone in Washington has to treat Stuart's recall as punishment for his cable. Against it, Ganon has resigned, and the cable has already reached Grace once without changing her course.

The theory: Todd Penn (Bradley Whitford) breaks with his wife, President Grace Penn (Allison Janney). The doubts are already on screen. Grace steers Todd to London as special envoy, partly so she no longer has to deal with him probing into her mental health, and he later confronts her about her behaviour.

Whitford told The Hollywood Reporter: "I think there may be a big part of Todd that would love to walk out." For that to happen, Todd would have to put his worries about Grace ahead of his loyalty to her.

Almost everything else he does points the other way. He passes information about Kate Wyler (Keri Russell) to Grace, and in a meeting with the British he raises the possibility of the US harming British citizens who stand in the way of its warships. Showrunner Debora Cahn put Todd's position plainly to The Hollywood Reporter: "He's a guy who took an oath to her."

The theory: Hal Wyler (Rufus Sewell) wants the presidency for himself. This theory is ShatteredBulbs' reading of the character, not something the show states.

After President Grace Penn (Allison Janney) is shot, he gets a taste of the job, temporarily taking on presidential duties while she recovers. Keri Russell, who plays his wife, told TVLine of that period: "It's the closest they have been to what they both really wanted: to be that close to power, to be in the room."

In our reading, Hal is the cleverest of the central four, a manipulator and a loose cannon at once. Staying vice president would keep him central to any attempt to invoke Section 4, which could make him Acting President but would not remove Grace or make him president in his own right. Showrunner Debora Cahn sees a different motive, telling TV Guide: "I don't think he chooses his wife; I think he chooses right versus wrong as he understands it."