Boris Johnson is expected to become Britain's next prime minister this week, vowing to deliver Brexit on Oct. 31 come what may, in the face of fierce opposition in Parliament. The postal ballot of 160,000 grassroots party members is expected to return Johnson, 55, as the new Conservative leader over Foreign Secretary Jeremy Hunt when the result is announced tomorrow. Bookmakers give Hunt around a one in 15 chance of victory.

The prime minister is due to take office Wednesday in a smoothly choreographed political handover. The new leader could face a challenge before he's even had a chance to unpack. The opposition Labour Party is considering calling a no-confidence vote in the Conservative government on Thursday. It would only take a handful of Conservative rebels to defeat the government and — unless it can overturn that vote within 14 days — trigger an early election. The good news for the prime minister is that Parliament is due to start its six-week summer break on Friday, and Labour will probably decide to wait until the fall before making a move.

Johnson, who sometimes has an ambiguous relationship with facts, campaigned with characteristic bluster, vowing to revive the country's "mojo" and making one main promise: Britain will leave the EU on Oct. 31, "come what may." He may find that promise hard to keep. The new leader heads a government with no parliamentary majority in a deeply divided country that is facing off with a mistrustful EU.

The crisis could come to a head at an EU summit on Oct. 17, just two weeks before Brexit day. EU leaders are sick of the Brexit drama and could resist if Britain asks for a further delay. Newly elected European Commission President Ursula von der Leyen says Britain can have an extension if it's for a strong reason such as an election or a new referendum.

Britain is not scheduled to have an election until 2022, but could hold an early poll if the government loses a no-confidence vote, or if the prime minister calls one to seek a mandate for his version of Brexit. An election might shake up Parliament and break the Brexit deadlock, but could also result in yet another divided legislature. Another potential deadlock-breaker, a new referendum on Britain's EU membership, could settle the issue, or prove as divisive as the last.

Once Britain does leave the bloc, its leader faces a fresh set of challenges in negotiating new trade deals around the world. The most coveted deal is with the U.S., but "America First" President Donald Trump is guaranteed to drive a hard bargain. A visit to Washington will be high on the new prime minister's agenda. Trump has warmly praised Johnson, but he can be a fickle friend. Last month, Johnson said the American president had "many good qualities."