A political escape artist finds his career on the brink.

When Boris Johnson won a landslide election victory for his Conservative Party in 2019, he loomed as a colossus over British politics, the man who had redrawn the country’s political map with a vow to “get Brexit done.”

With an 80-seat majority in Parliament, the greatest amassed by a Conservative leader since Margaret Thatcher in 1987, he seemed assured of five years in power. Some analysts predicted a comfortable decade in 10 Downing Street for Mr. Johnson, the most reliable vote-getter in British politics.

On Monday, less than three years after that triumph, Mr. Johnson’s future was hanging by a thread. Rebels in his party have called for a no-confidence vote that could cost him his job; even if he wins and clings to his position, it could cripple him as an effective and credible leader. He faces that vote from his own party Monday night.

It is one of the most head-spinning reversals of fortune in modern British political history.

What happened?

To some extent, Mr. Johnson’s standing crumbled because of the same baffling mix of strengths and foibles that propelled his rise: rare political intuition offset by breathtaking personal recklessness; a sense of history that was not matched by a corresponding sense of how he should conduct himself as a leader; uncanny people skills vitiated by a transactional style that earned him few allies and left him isolated at dangerous moments.

It is that last quality, analysts say, that made Mr. Johnson so vulnerable to the setbacks he has suffered. With no underlying ideology beyond Brexit and no network of political friends, the prime minister lost the support of lawmakers in his party when it became clear they could not count on him to win the next election.

“Johnson’s such an accomplished escape artist, and his colleagues so craven and cowardly that you can’t rule out him living to fight another day,” said Tim Bale, a professor of politics at Queen Mary University of London. “But for what precisely? ‘There’s no there there,’ as the saying goes.”