LONDON (AP) — Liz Truss' resignation as British Prime Minister on Thursday triggered another leadership race — the second in just four months — for the U.K.'s fractured and demoralized Conservative Party.

Truss, who quit after just 45 days in office, said her successor will be chosen in a leadership contest to be completed by the end of next week. Graham Brady, a senior Conservative lawmaker who oversees the party's leadership challenges, said each candidate must secure 100 nominations from legislators to run and that the race will conclude by next Friday.

Former Treasury chief Rishi Sunak, ex-Cabinet minister Penny Mordaunt and Defense Secretary Ben Wallace are among those considered credible contenders for the top job. Former Prime Minister Boris Johnson may also return. Jeremy Hunt, who has been brought in as new Treasury chief to steer the economy, has ruled out running.

Whoever wins will become the fifth British prime minister in six years.

Here's a look at the potential runners and riders:

RISHI SUNAK, FORMER TREASURY CHIEF

Sunak, 42, came second to Truss in the last Conservative leadership race, gathering 60,399 votes compared to her 81,326.

He quit as Treasury chief in July, in protest against then-Prime Minister Boris Johnson's leadership. In the contest to replace Johnson, Sunak positioned himself as the candidate who tells hard truths about Britain's public finances. He argued that climbing inflation must be controlled first, and called promises by Truss and other rivals to immediately slash taxes reckless "fairy tales."

Sunak was proved right when Truss' unfunded tax-cutting economic stimulus package tanked the British pound and triggered chaos in the markets in September.

Sunak became Treasury chief in 2020 and steered Britain's slumping economy through the coronavirus pandemic. He oversaw billions of pounds in government handouts to help businesses and workers hard hit by COVID-19.

Sunak was regarded by many as the Conservatives' brightest rising star. Born to Indian parents who moved to Britain from East Africa, Sunak attended the exclusive Winchester College private school and studied at Oxford. Some see his elite education and work for the investment bank Goldman Sachs and a hedge fund as a liability because it makes him seem out of touch with ordinary voters.

In the past year he faced heavy criticism for being slow to respond to Britain's cost-of-living crisis. His reputation also took a hit after he was fined by police for attending a lockdown-flouting birthday party at Downing Street in June 2020.

Some also criticized him following revelations that his wife, Akshata Murthy, avoided paying taxes on her overseas income.

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PENNY MORDAUNT, HOUSE OF COMMONS LEADER

Mordaunt, 49, came third after Sunak and Truss in the last Tory leadership race, when she ran with a campaign named "PM 4 PM." Mordaunt did not hold a senior post in Johnson's Cabinet, and she positioned herself as offering a clean break from his scandal-tainted government.

A former international trade minister, Mordaunt is popular among Conservative lawmakers. Some believe she could be the right candidate to help heal the party's divisions. But she is largely an unknown figure to most Britons, and outside Conservative circles she remains best known for appearing on the 2014 reality TV show "Splash!"

Mordaunt played a prominent role in the pro-Brexit campaign. She was the first woman to become British defense secretary in 2019 -- though she was removed by Johnson after just three months in the post because she had backed another candidate for party leader, Jeremy Hunt.

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SUELLA BRAVERMAN, EX-HOME SECRETARY

Braverman, 42, resigned as Home Secretary late Wednesday, with a scathing letter criticizing Truss' "tumultuous" premiership. Her move kicked off a chaotic night in British politics that ended in Truss' resignation hours later.

A former barrister who became England's attorney general in 2020, Braverman was the first to put her hat in the ring during this summer's leadership race to replace Johnson.

During her short tenure as Home Secretary, a top government post overseeing immigration and counterterrorism, Braverman vowed to crack down hard on asylum seekers, saying it was her "dream" to see a flight deporting those seeking refuge in Britain to Rwanda. She also wanted to pull the U.K. out of the European Convention on Human rights.

She made headlines — and was mocked by opponents — when she complained recently in Parliament that travel disruptions caused by trade union strikes were to be blamed on left-wing, "tofu-eating wokerati."

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BEN WALLACE, DEFENSE SECRETARY

Wallace, a 52-year-old army veteran, is popular within the Conservative Party. He has won admirers for his straight talk, particularly among Conservative lawmakers who pressed for the U.K. to increase its defense spending.

Wallace has raised his profile as a key government voice in Britain's response to Russia's war in Ukraine. But he recently said he wanted to remain in his current job. Earlier this week, he reportedly said "I want to be the Secretary of State for Defense until I finish" when asked if he wanted the top job.

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BORIS JOHNSON, FORMER PRIME MINISTER

There was intense speculation Thursday that Johnson, 58, may return and put himself forward as prime minister again — just weeks after he was forced out of office by a series of ethics scandals.

Within hours of Truss' resignation, several Conservative allies of Johnson's voiced their support for him to return.

"The only person who has a mandate from the general public is Boris Johnson," said one lawmaker, Marco Longhi. "He is the only person who can discharge the mandate from the people."

Johnson led the Conservatives to their biggest win in decades in the 2019 general election, largely on the back of his promise to "get Brexit done."

But his time in office was overshadowed by scandals over alcohol-fueled parties held at his official residence while national COVID-19 restrictions were in place. He still faces an ongoing investigation by Parliament's privileges committee into whether he lied to lawmakers about COVID-rule breaking at Downing Street.

He was forced to announce his resignation on July 7 after former allies in his Cabinet joined a mass exodus of government officials protesting his leadership.

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