Cameron will be gone as of early September, and jostling for the top job has begun. Over the next few weeks, Conservative Party lawmakers will whittle the field of contenders down to two candidates, and then the wider party membership will choose Cameron's successor.
This is a rocky time in British politics, and predicting the future a fool's game. But the race, as it stands today, is being cast as a Boris Johnson vs. Anyone But Boris Johnson contest.
Here are some of the leading candidates, according to bookmaker William Hill.
Britain’s Conservative Party may have suffered a terrible blow with the resignation of Cameron, its leader, but you know that old saying: When one door closes, another opens with a tousle-haired politician grinning gleefully in your direction.
All eyes are now on Boris Johnson, the charismatic lawmaker and face of the “leave” campaign. Johnson, the former mayor of London and long-term frenemy of Cameron, took a massive gamble when he decided to campaign for “leave,” but it seems to have paid off handsomely. Bookies say he's the clear favorite to become the next British prime minister.
He also has the backing of Britain's justice secretary, Michael Gove — or “Gover” as Johnson calls him. Gove was one of the leading figures in the "leave" campaign and would likely get a top job in a Johnson-led government.
If Johnson did fill Cameron's shoes, he would presumably seek to unite a divided country that voted 52 to 48 for “leave.” That could prove a challenge in pro-E.U. London. When Johnson left his house after the results of the vote came in, the mood on the street was not one of bonhomie.
But when Johnson finally made his way through the jeering crowd, and past these cyclists, he appeared statesmanlike as he addressed the nation and paid tribute to Cameron.
Theresa May, Britain’s home secretary, campaigned for the U.K. to remain in the E.U., though she didn’t take center stage. She is seen as an effective operator at the Home Office, which oversees the vexing issue of immigration, and the front-runner among those in the Anyone But Boris camp.
Mujtaba Rahman, a European analyst with the Eurasia Group, said in a recent briefing note that a leadership contest would likely boil down to a race between Johnson and May.
May “is competent and is well-liked by her peers in Europe, who believe, correctly, she will be a less awkward negotiating partner than Johnson,” he wrote.
On Wednesday, Britain’s work and pensions secretary became the first to officially launch his leadership campaign. Although he was in the "remain" camp, in a speech on Wednesday he ruled out a second referendum and said that controlling immigration would be a top priority in talks with the E.U. Unlike the Eton-educated Johnson, Crabb has humble roots — he was raised by a single mom on a council estate — and says he will run on a “blue collar” ticket with Sajid Javid, the business secretary.
The energy secretary actively campaigned alongside Johnson for the U.K. to leave the E.U. She has support from Brexiters unsure whether Johnson will put an end to freedom of movement for people from the E.U. (In his Daily Telegraph column on Monday, Johnson wrote: "It is said that those who voted Leave were mainly driven by anxieties about immigration. I do not believe that is so.")
“Free trade with the EU will be in all our interests. But essential we agree free movement no longer applies to UK. Confident we can do this,” Leadsom recently tweeted.
Britain’s education secretary is thought to be mulling over whether to launch a bid for the keys to 10 Downing Street. The former lawyer has criticized the tone of some aspects of the pro-Brexit campaign and says the Conservative Party needs to stress the positive aspects of immigration.
Of course, any of these people could become the leader of something other than the United Kingdom — a union made up of England, Scotland, Wales and Northern Ireland — with Brexit triggering a number of existential questions for the U.K.
Nicola Sturgeon, the popular, pro-E.U. leader of the Scottish National Party, has vowed to seek a second Scottish independence referendum after the majority of Scots voted to stay in the E.U. On Wednesday, she was in Brussels pressing her case.
Is there a scenario, wonder curious minds on Twitter, where Sturgeon could become the next prime minister and maybe wind back the clock?
“Why can't Nicola Sturgeon be the new PM and tell the EU we made a mistake?” wrote one user. “Wishful thinking.”