LONDON (BLOOMBERG) - For Mr Boris Johnson, it's decision time.

After years of flirting with a challenge for the top job in British politics, the former foreign secretary will arrive at the Conservative Party's annual conference on Tuesday (Oct 2) to make a speech that shows whether he still has a chance - or the will - to be prime minister of a party at war with itself.

Tories say Mr Johnson doesn't have a formal campaign team, but the past week has seen a media blitz: a 4,600-word essay on his Brexit plan, television interviews to all channels, a front-page interview in the Sunday Times. On Monday, there was a jokey photo teasing Mrs Theresa May.

One of the recurring questions during this painful Brexit process is how a prime minister described so often as weak can endure in the face of regular threats of mutiny, specifically from Brexit purists so unhappy with the direction she has taken on divorce negotiations.

Tory opponents of Mrs May acknowledge privately that although they have sufficient numbers to initiate a challenge to the prime minister - they need 48 signatures - they don't have enough to pass the next hurdle, passing a motion of no confidence in her. For that, they need 158 lawmakers.

So even as Mr Johnson barrels into Birmingham, the feeling among senior figures is that he's been indulged for too long. On display this week was a fightback from Mrs May's team with ministers licensed to put the boot in.

Chancellor of the Exchequer Philip Hammond mocked him in a series of interviews as not having an alternative plan. Scottish Conservative Leader Ruth Davidson was scathing about his claim he was misled about the government's December agreement with the European Union. If she'd understood what it meant - and Ms Davidson is not in government - why hadn't he when he was a senior Cabinet minister at the time?

But late on Monday, Ms Arlene Foster, leader of Northern Ireland's Democratic Unionist Party which Mrs May relies on to govern, handed Mr Johnson a significant boost. In an interview with the Daily Telegraph, Ms Foster praised Mr Johnson's "belief" and "spirit" and said she'd be happy to work with him as prime minister.

"People want hope, they want to be positive," Ms Foster told the newspaper.

When Mr Johnson stands up at a fringe meeting at the conference on Tuesday afternoon - he isn't invited on the main stage - he will have to deliver a proper pitch for why he should lead the country. To do otherwise would be to admit defeat.

"He can't be the Grand Old Duke of York, marching his supporters up to the top of the hill only to march them down again," said his biographer Andrew Gimson. "He's got to be Henry V rallying his troops before Agincourt."

According to extracts of his planned speech, Mr Johnson will appeal to the "wealth creating sector of the economy - the people who get up at the crack of dawn to prepare their shops, the grafters and the grifters, the innovators, the entrepreneurs."

The tone is a far cry from when Mr Johnson was caught saying "f*** business" to a European diplomat in June, just as more companies were voicing their concern over Brexit.

"We Conservatives know that it is only a strong private sector economy that can pay for superb public services, and that is the central symmetry of our one nation Toryism," Mr Johnson will say Tuesday.

Mr Johnson's window for a challenge is narrowing with younger rivals like Dominic Raab making a good impression. Most Tories agree that they will want a change of leader before the next election - scheduled for 2022 though the opposition is eager for one much sooner than that.

But Mr Johnson's best pitch for the leadership is that he would be willing to deliver a fuller Brexit than Mrs May. That argument only holds as Mrs May struggles to get deal agreed with the EU and she wants to close that loop before the end of November.

Mr Johnson's star could already be fading. An informal vote at a fringe by the pro-Brexit Bruges Group found those present backing another lawmaker, Mr Jacob Rees-Mogg, over him by a ratio of two to one.

Later, at the same event, former International Development Secretary Priti Patel gave a speech that left the impression she too would challenge for the pro-Brexit ticket in any leadership contest.

But a strong speech from Mr Johnson might overturn all of those objections, especially if it was followed by a weak one from Mrs May on Wednesday. Last year's address was a debacle for her - with the set collapsing around her as the prime minister succumbed to a coughing fit.

Government ministers at conference were openly scornful of his chances. "Boris isn't a serious candidate at all," Business Minister Richard Harrington said in an interview. "People laugh at old-fashioned English eccentricity, they laugh at Latin, they laugh at jokes, but they don't want it in a leader of the Conservative Party. I've seen little support for him in the Parliamentary party, and I think the membership have got more sense." But the very fact that ministers are licensed to attack Mr Johnson shows those around Mrs May are taking the threat seriously.

And plenty of the membership disagree with Mr Harrington. Mr Johnson is booked into a hall with a capacity of 1,500 seats, and it's expected to be full. One of those trying to get in will be 82-year-old James Gibbs, a rank-and-file member who had travelled to the conference from his home in Cyprus.

"I think we are sadly lacking in people who inspire you," he said. "Boris is seen as a winner. If we want to keep this show on the road that means Boris."