British leader faces a no-confidence vote

Members of Prime Minister Theresa May’s Conservative Party are scheduled to hold a ballot in Parliament tonight, a new and potentially lethal threat to her leadership.

Under party rules, Mrs. May needs to win 158 votes from the 315 Conservatives in Parliament to stay as party leader and therefore prime minister. If she does, party members can’t challenge her leadership again for a year. If she loses the vote, she must withdraw and another leader will be chosen over the coming weeks.

Why now: Mrs. May’s prospects have been endangered by the crisis over her negotiations on Britain’s withdrawal from the European Union and her decision on Monday to postpone a crucial parliamentary vote.

Explainer: We examine some of the possible replacements if Mrs. May loses tonight’s vote.

News analysis: Britain, France and Germany are all facing political change or upheaval. For the European Union, the question is who will guide the bloc into an uncertain future. Our chief diplomatic correspondent reports from Brussels.