LONDON — After Theresa May’s three-year nightmare as Britain’s prime minister, you might think that no one would want her job. But as the race formally got underway on Monday, no fewer than 10 candidates secured enough support from Conservative lawmakers to enter the contest, a battle already marked by fierce infighting and lurid headlines over the candidates’ past drug use.

The field is so crowded that the Tory party modified its rules to try to whittle the contenders down to a shortlist of two by June 20.

The final choice will be made by around 150,000 members of the Conservative Party (the exact total is something of a mystery), producing a new prime minister by the end of next month. Here is what to expect.

Is Boris Johnson a surefire winner for the Conservatives?

It is considered Boris Johnson’s race to lose. But in light of the fact that, within recent memory, none of the early favorites have gone on to win a Tory leadership contest, predictions at this point are perilous.