Boris Johnson announced late on Sunday that he would not be standing for the leadership of the Conservative Party, and by extension another stint as British prime minister.

This put Johnson's former Finance Minister Rishi Sunak seemingly in prime position to seek the job. Sunak is one of two politicians, along with Penny Mordaunt, to have officially expressed a desire to run, and the only candidate who had more than 100 public endorsements from Conservative lawmakers, the minimum threshold to qualify for the role.  

What did Johnson say? 

Johnson said that he had been "overwhelmed by the number of people who suggested that I should once again contest the Conservative Party leadership" in the last few days, following Liz Truss' resignation after just a few weeks in office. 

He said he believed he was "uniquely placed to avert a general election now," and that he had cleared the "very high hurdle of 102 nominations, including a proposer and a seconder" required to qualify for the contest.

"But in the course of the last days I have sadly come to the conclusion that this would simply not be the right thing to do. You can't govern effectively unless you have a united party in parliament," Johnson said.  

He said he would therefore not allow his nomination to go forward and said he would commit his support to "whoever succeeds," suggesting he did not intend to endorse anybody else. 

He appeared to leave the door open for some later return, concluding the message to supporters: "I believe that I have much to offer but I am afraid that this is simply not the right time."

Path cleared for Rishi Sunak? Mordaunt still in contention

Johnson's announcement adds further weight to the leadership bid of bookmakers' favorite Rishi Sunak. 

Sunak is one of two candidates to have declared, and the only one who more than 100 Conservative MPs have publicly backed. He sought to strike a conciliatory tone after his rival's announcement. 

"Boris Johnson delivered Brexit and the great vaccine rollout," Sunak wrote on Twitter. "He led our country through some of the toughest challenges we have ever faced, and then took on Putin and his barbaric war in Ukraine. We will forever be grateful to him for that." 

Sunak went on to say, "Although he has decided not to run for PM again, I truly hope he continues to contribute to public life at home and abroad."

One of Johnson's higher-profile public backers to declare on Saturday had been Nadhim Zahawi. He had a brief but memorable tenure as Johnson's finance minister following Sunak's resignation back in July, before himself calling on Johnson to quit roughly 48 hours after his appointment. Late on Sunday, he took to Twitter once more to say he would now switch his support from a Johnson comeback to Sunak. 

"A day is a long time in politics," Zahawi wrote. "Given today's news, it's clear that we should turn to Rishi Sunak to become our next prime minister."  He said Sunak would have his "full support and loyalty." 

Why all this talk of 100 lawmakers' support?

The high threshold of 100 MPs' support is a new rule the party has introduced, changing its existing leadership election standards in a bid to avoid continued division in a party that has now toppled two of its own prime ministers in a matter of months. 

There are 357 Conservative MPs, however, meaning that in theory, the other candidate Penny Mordaunt might be able to secure enough support to contest the leadership with Sunak. As of Sunday evening, Mordaunt had 24 declared backers.

If more than one person qualifies by the 2 p.m (1300 UTC/GMT) deadline on Monday, the Conservatives plan to hold an online members' vote to pick a winner.

Johnson said that he had held talks with both Sunak and Mordaunt "because I hoped that we could come together in the national interest," but said "we have sadly not been able to work out a way of doing this." 

Shades of June 2016

Sunday's statement had echoes of June 30, 2016, barely a week after the Brexit referendum. At the time, Johnson was seen by many as a likely candidate to run to succeed David Cameron having been the front man for the "Leave" campaign. 

Johnson went through a furious process of drumming up support for a campaign, only to hold a press conference in which he said he had come to the conclusion that "that person cannot be me."

Why aren't there just new elections? 

It's extremely common in Britain for prime ministers not to rise or fall at the ballot box.

No British prime minister since Edward Heath (1970-74) has entered and left 10 Downing Street as the direct result of elections.

Labour's Gordon Brown was the last politician to lose the job at the ballot box, in 2010. 

Given that the prime minister is appointed by a majority of MPs, it's possible for parties to seek to change leaders during a term in office. 

Opinion polls currently suggest that if elections were held right now, as the opposition Labour Party says they should be, the Conservatives would fare very poorly after a tempestuous few months, no matter who was leading the party. 

Assuming they can maintain a stable government in the mean time, elections do not have to take place until January of 2025 at the latest. 

msh/jsi (AFP, dpa, Reuters, AP)