A former banker whose father worked as a bus driver, Mr. Javid is at the top of some polls of potential party leaders. But he is less than fully trusted among fervent supporters of Brexit, who believe that other contenders worked harder behind the scenes to advance their cause.

Michael Gove

Mr. Gove helped lead the campaign for leaving the European Union in 2016, famously arguing that Britons had had “enough of experts” telling them what was best. He has since become one of the most reliable salespeople for Mrs. May’s deal, remaining in the prime minister’s cabinet as environment secretary over the protests of some of his allies in the referendum campaign.

When the Conservatives last chose a new leader, in the wake of that campaign, he torpedoed Mr. Johnson’s candidacy with a late decision to enter the race himself, and the reputation he earned then for stabbing allies in the back (or the front, as some argued) has stuck with him. Mr. Gove is now seen as having a narrow route to the party leadership, with pro-Brexit politicians angry at him for standing behind Mrs. May’s deal and pro-Europeans angry at him for backing Brexit.

Amber Rudd

Ms. Rudd — a close ally of Mrs. May who was forced to resign as home secretary but has since returned to the cabinet as work and pensions secretary — is a leader of the “soft Brexit” Conservatives who favor maintaining close ties with the European Union, and is seen as one who could prevent Mr. Johnson from taking over leadership.

While Ms. Rudd supports the prime minister’s proposed Brexit deal, she became the first minister to publicly discuss a “Plan B” should the proposal not pass through Parliament. Her supporters believe that she could build a consensus in Parliament over a new approach to Brexit.

But that stance would be unlikely to find favor among grass-roots party members. There are also concerns over the fact that she holds a tiny majority in her Hastings and Rye constituency; the prime minister needs to be in Parliament, and she might lose her seat at the next general election.

Jeremy Hunt

Mr. Hunt, the foreign secretary, is not widely considered a popular first choice but many people’s second choice, one who would be acceptable to many factions in the party. Though he voted for Britain to remain in the European Union in the 2016 referendum, he has since cultivated a reputation as an outspoken Brexiter. Despite that change of heart, or perhaps because of it, he remains suspect in many Conservatives’ eyes.

He backed Ms. May’s proposed Brexit deal and, like most in the cabinet, has condemned the challenge to her leadership, saying that she is the best person to make sure that Britain leaves the European Union on March 29.