After surviving the loss of her parliamentary majority last year, Prime Minister Theresa May faces perhaps her most decisive test next week, when lawmakers decide whether to accept or reject her deal with Brussels on Britain's departure from the EU.
May has clung to power since June 2017, when only 42 per cent of voters backed her Conservative Party.
The results were a stunning blow to her Brexit plans and leadership, forcing her to run a minority government propped up by 10 lawmakers from Northern Ireland's Democratic Unionist Party (DUP).
The prime minister appears unlikely to win much more than 42 per cent of votes in parliament when lawmakers in the Commons vote on her deal on Tuesday (local time).
May has insisted that the choice on offer is her deal or no deal, but pro-EU lawmakers reject that "false dichotomy" and want parliament to consider other options.
Eurosceptic Conservatives, on the other hand, say that May has negotiated a "Brexit in name only".
She insists the deal "fulfils the wishes of the British people" after a 52-per-cent majority voted to leave the EU in the 2016 Brexit referendum.
But many pro-EU and pro-Brexit lawmakers among the 315 Conservatives in the 650-seat house reject that argument.
The DUP opposes the deal on the grounds of a temporary backstop measure to guarantee an open Irish border after Brexit. The backstop could place Northern Ireland under slightly different trading arrangements from the rest of the United Kingdom.
What happens if, as expected, parliament rejects May's deal, could depend on "how badly, and in what way, she loses," said John Curtice, a political scientist at the University of Strathclyde.
A narrow defeat of 20 votes or less "would almost be a moral victory" that could allow her to tweak the deal - perhaps on the key issue of the backstop - before going back to parliament, Curtice said.
The result will depend on whether there are "more Labour supporters of the government than there are Conservative opponents of the government," Conservative right-winger Jacob Rees-Mogg, who leads a group of several dozen eurosceptic lawmakers, told the political news website Conservative Home.
Labour's 257 members of parliament will oppose May's deal, Left-wing leader Jeremy Corbyn said, and only a few Labour rebels are expected to back May.
"It [May's deal] is a worst-of-all-worlds deal that works for nobody, whether they voted leave or remain," Corbyn wrote in Friday's Guardian newspaper.
"We are working with MPs and parties across the House of Commons not only to ensure it is rejected, but also to prevent any possibility of a no-deal outcome," Corbyn said.
He said Labour wants Britain to stay in a customs union and keep "a new and strong relationship with the single market" after Brexit.
"Labour's view at the moment seems very much more strongly centred around the possibility of collapsing the government, rather than saving a deal," said Simon Usherwood, a Brexit-focussed political analyst at the University of Surrey.
A growing number of Labour and Conservative lawmakers are backing the People's Vote campaign for a second referendum - an option that May has ruled out.
Corbyn has suggested it would only be a last resort for Labour, which hopes to force an election instead.