Three ways Boris Johnson could become Britain's shortest-serving prime minister

LONDON - Prime Minister Boris Johnson has been in office less than a month, and already Britain's chattering classes are talking about his demise.

Johnson has promised to get Britain out of the European Union, with or without a Brexit deal, in his first 100 days.

But can he remain in No. 10 Downing Street beyond 119 days - the tenure of the United Kingdom's most fleeting prime minister, George Canning, who served from April to August in 1827?

Perhaps. Theresa May survived in office for two years after her first round of political obituaries were written.

Here are three scenarios being batted around for how Johnson could go.

- Johnson could lose a no-confidence vote and resign. Opposition Labour Party leader Jeremy Corbyn has said he would call for a no-confidence vote against Johnson to stop an abrupt "no-deal Brexit" - which Johnson has said Britain must prepare for and which economists say could lead to turmoil on both sides of the English Channel.

Corbyn could call for a vote as early as the week of Sept. 3, when members of Parliament return from their summer recess. He said he would introduce the motion at an "appropriate very early time" and "at a point when we can win it."

How realistic is a Johnson loss? Well, he has a working majority in Parliament of just one seat, and a few lawmakers from his Conservative party have indicated that they'd consider the nuclear option of voting against their own government if that's what it took to avoid a no-deal Brexit. But there are also independent lawmakers and Brexit-backing politicians from the Labour Party who might support the prime minister in a no-confidence vote.

To let the hypothetical play out, though: If Johnson lost, lawmakers would have 14 days to form an alternative government that could command a majority in the House of Commons. Labour's John McDonnell suggested Corbyn should hop in "a cab to Buckingham Palace to say, 'We're taking over.' " He may not have meant that literally, but Corbyn would certainly try to win the backing of the majority of lawmakers.

It's unclear if Corbyn - or anyone else - could muster a majority. But if they did, Johnson would come under extreme pressure to resign.

- Johnson could lose an election. Britain's next general election is scheduled for 2022, but there are a few ways it could end up with one much sooner.

If Johnson lost a confidence vote and if no other viable government emerged in that two-week window, Parliament would be dissolved and an election would be held 25 working days later.

Alternatively, Johnson might want to call an election of his own volition - either to strengthen his mandate to push Brexit through (if Parliament somehow managed to block him) or to capitalize on any bounce after having made Brexit happen. Either way, he'd no doubt like to improve that one-seat majority.

Johnson has ruled out an election before the Brexit deadline of Oct. 31. Some of his allies have reportedly said he could set a date for early November. Michael Gove, who is in charge of no-deal Brexit planning, raised eyebrows with his suggestion that Nov. 1 should be a banking holiday, to limit market panic in the wake of no-deal. Could that be a date they're eyeing for an election? It would have the advantage of taking place before voters feel the destabilizing effects of crashing out without a deal to manage the withdrawal.

Corbyn has cried foul, nodding to the convention that governments don't make major policy decisions during a general election campaign. But Johnson isn't the most conventional politician.

So how might Johnson and his Conservatives fare in an election? Recall that Johnson has yet to face the British electorate - he was selected by a small contingent of dues-paying members of the Conservative Party, who skew older, whiter and more male.

Conservatives were trounced in spring elections for the European Parliament and in local races. But the latest YouGov polling indicates support for the party is up since Johnson became prime minister. Asked about hypothetical voting intentions, 31 percent said Conservative, 22 percent said Labour, 21 percent said Liberal Democrat and 14 percent said Brexit Party.

If Johnson could sell the idea that Parliament was thwarting his effort to deliver the Brexit the people voted for, he might be able to swing even more support his way, winning back defectors from Nigel Farage's Brexit Party. But if he pursued a no-deal Brexit and chaos ensued, he could see his support evaporate. In that case, pro-E. U. voters - who are scattered across a number of parties - might come together to oppose him.

- Johnson could lose a no-confidence vote, refuse to resign and get sacked by the queen.

One imagines that Queen Elizabeth II wouldn't want to touch the hornet's nest that is Brexit with a 10-foot pole. The British monarch is famously neutral when it comes to all things politics. Even when she obliquely references Britain's relationship with the European Union, she does so in a queenly, uncontentious way.

But there is speculation that the 93-year-old monarch may get sucked in.

Johnson has repeatedly refused to say what he would do if he lost a no-confidence vote. If Corbyn or someone else formed a viable alternative government, and if Johnson still refused to budge, then some say the queen could effectively sack Johnson.

The queen "is not a decorative extra," Conservative Dominic Grieve, a former attorney general, told the Times of London. "It's true she has sought to keep herself well away from the cut and thrust of politics but at the end of the day there are residual powers and responsibilities which lie with her. She might have to dispense with his services herself."

David Howarth, a professor of law and public policy at the University of Cambridge, told LBC Radio that the queen could in theory fire Johnson, but that, more likely, Johnson would be asked to step aside so as not to "embarrass" her.

Tony Travers, a government professor at the London School of Economics, is also among the skeptics. "I find it hard to believe that the queen as an individual would want to make a decision that changed the government of the country," he said.

When was the last time a monarch interfered with the choosing of a prime minister? That would be in 1834, when King William IV dismissed William Lamb. Six months later, Lamb was reappointed as prime minister, and he went on to become one of Queen Victoria's closest advisers

Queen Elizabeth II is unlikely to be losing any sleep over this scenario at this point. She is officially on holiday at Balmoral Castle in Scotland. But royal watchers say she stays abreast of the news, which this past weekend included this front-page headline in the Daily Telegraph: "Buckingham Palace and Downing Street plan to keep the Queen out of looming constitutional crisis over Brexit."