London (CNN) Boris Johnson's job just got even harder.

The UK Prime Minister's first full week in office ended on a very sour note, when one of his own lawmakers was robbed of their parliamentary seat in a special election . Despite a surge for his Conservative party in opinion polls, breathless reports of a "Boris bounce" appear to have been premature.

The Conservatives' share of the vote in the Brecon and Radnorshire region of Wales fell by nearly 10 percentage points, as they came in second behind the pro-European Liberal Democrats. The result leaves Johnson with a working parliamentary majority of just one.

Johnson already faces the toughest challenge of any leader since the end of World War II: to deliver Brexit on October 31 and unite a bitterly divided nation.

Despite all his pro-Brexit rhetoric, Johnson has inherited all the problems that ultimately did for his predecessor, Theresa May. And not having a majority is probably the biggest of all these headaches.

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