When Conservative Party members selected Boris Johnson as their prime minister, they were looking nervously over their shoulders at the success of Nigel Farage’s Brexit Party.

Who better to unite “leavers” than one of the architects of Brexit? Who better to beat Labour Party leader Jeremy Corbyn than the man who won two mayoral races in Labour-leaning London? They certainly were not thinking about Jo Swinson and her Liberal Democrat party. Perhaps they should now.

Swinson became party leader last week after a landslide victory against a more experienced former minister, Ed Davey. At 39, she may be a borderline millennial, but she is no neophyte. She contested a seat for Parliament at just 21, lost twice before finally becoming the first Lib Dem to win her seat of East Dunbartonshire in Scotland in 2005. At 25, she was the youngest member of the House of Commons.

While Johnson is a household name, Swinson isn’t. Less than a third of people in her own country seem to know who she is. But her party is enjoying a strong revival — thanks to its unequivocal opposition to leaving the EU, encapsulated in its “bollocks to Brexit” slogan in the European parliamentary elections in May.

It is a message aimed squarely at opponents of Brexit in both the Conservative and Labour parties, and those who are unhappy with their respective leaders’ baggage. Johnson is viewed as slipshod by his detractors, while Corbyn has been dogged by allegations of anti-Semitism among his supporters and opposition to his policies of nationalization. “Voters don’t like split parties,” says Nick Barlow, a researcher at Queen Mary University of London and Liberal Democrat councillor. “They often punish them at the polls as happened to the Conservatives in 1997 and Labour in the 1980s.”

Of Britain’s three main political parties, the Liberal Democrats have perhaps come to terms with Brexit the most. Labour’s initial support for leaving has given way to something more confused, while Conservative lawmakers disagree about whether to leave without a deal. A willingness to brave a no-deal exit was the litmus test for joining Johnson’s team.

This reinvention seems to be working. The Liberal Democrats are now polling second, at 23 percent — just two points behind the Conservatives and ahead of Labour. Their 20 percent share of the vote in May’s European parliamentary elections was second only to that of the Brexit Party. The grouping has already benefited from some defections, and a handful of Conservative MPs are reportedly flirting with the same thing.

If, as many expect, an early general election (or second referendum) becomes inevitable, because Parliament seeks to thwart the prime minister’s no-deal plan, the resurgent Lib Dems stand to inflict the most damage on Johnson’s Conservatives. While the Liberal Democrats will pick up disgruntled Labour voters, thanks to the peculiarities of Britain’s winner-takes-all electoral system, they have a more realistic chance of winning in Conservative constituencies. It is in those seats that Swinson will want to focus her firepower and, in that sense, Johnson’s all-in support for a no-deal Brexit is a gift.

Swinson’s challenge will be to stay focused on her “remain” message while increasing the profile of other Liberal Democrat figures and building a distinctive manifesto.

She will be aware that her party has squandered its chances before: Back in 2010, her party entered government as junior coalition partner with the Conservatives. Five years later, it was nearly wiped out after being inextricably linked with austerity and increasing university tuition fees. Under Tim Farron, the party added only four seats at the 2017 election as its campaign was overshadowed by its leader’s illiberal views on abortion and gay sex.

Swinson’s success, though, will depend greatly on Johnson failing. The Tory leader will be in trouble if he cannot hold his own party together, win concessions from the European Union, convince enough of Parliament to back his preferred outcome, or win a second public vote.

Having just seen off one female party leader, Johnson may find there’s another he can no longer ignore.

Therese Raphael writes editorials on European politics and economics for Bloomberg Opinion. She was editorial page editor of The Wall Street Journal Europe.

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