Both men share the same elite education at Eton College, Britain’s most famous private school, and Balliol College at Oxford University, but their politics are far apart.
Charismatic, entertaining and often shambolic, Mr. Johnson was the figurehead for the Leave forces in the 2016 Brexit referendum that triggered three years and counting of political turmoil.
Most analysts think that, with the Conservatives now facing a fierce challenge from the right in Nigel Farage’s Brexit Party, Mr. Johnson’s campaign is unstoppable. His hard-line stance on Brexit equips him to take on Mr. Farage’s new right-wing insurgents, and Mr. Johnson’s campaigning skills also make him the man to beat the leader of the opposition Labour Party, Jeremy Corbyn, the argument goes.
If he can make the shortlist of two, something that now seems assured, Mr. Johnson should have one foot in Downing Street. He is wildly popular among Conservative Party activists who will make the final choice and who desperately want to leave the European Union as soon as possible. Mr. Johnson promises that Britain will leave on Oct. 31 when the next Brexit deadline expires, although he is rather vague as to how this would happen.
For Mr. Stewart, who was promoted to the cabinet only last month, even to make it to the final shortlist of two would be a spectacular achievement, yet his prospects are growing, according to the bookmakers.
Mr. Johnson has been accused of hiding from scrutiny after ducking a TV debate with his opponents and another face-to-face with political reporters, and his complicated personal life has also been used by opponents to question his reliability and trustworthiness.
After Matthew Parris, a commentator and former Conservative lawmaker, asked on a BBC radio show how many children Mr. Johnson has, the issue has bubbled along without resolution. When Mr. Johnson failed to show up on Sunday at a Channel 4 debate with the other candidates, some articles joked caustically that it was Father’s Day in Britain and that he had many other places to be.