PARIS — There are smiles, and then there are mile-wide victory grins. On the day Britain voted to leave the EU, French far-right leader Marine Le Pen couldn't wipe the latter from her face.

Brexit had "given [her] wings," Le Pen told glossy magazine Paris Match a few days later, while underlings reported they had rarely seen her so "happy and energized."

It's easy to understand why the vote lifted her spirits. After a tough year marred by a bitter public feud with her father, an election defeat and constant squabbling in her party, Britain's vote to leave brought much-needed validation.

But as the first flush of Brexit subsides, Le Pen faces a big challenge. Over the next 10 months, she will have to prove that France should also leave the European Union, while widening her electoral base enough to get 51 percent of the vote and take over the presidency.

Does Brexit improve her chances of becoming French president in 2017? According to a pollster, a National Front expert and officials inside the party, the simple answer is 'No' — not unless Brexit turns out to be a runaway success for the U.K.

Brexit may even make the path ahead trickier as mainstream candidates raid Le Pen's anti-EU toolbox for ideas; concerns about post-Brexit uncertainty work against her; and France's dominant parties close ranks to keep the National Front out of power.

"The honeymoon was over by Monday morning," said Jérome Fourquet, an analyst at the Ifop polling agency.

"In France there is no majority for leaving the EU. Even if people are Euroskeptic, they understand that getting out is complicated and messy, even more so with Britain's example."

The problem with Brexit

An immediate problem for Le Pen is how to turn Brexit into a persuasive political argument at home.

Before the vote, France and Britain shared similarly high levels of Euroskepticism, with a Pew Research poll showing that mistrust of the EU was even higher in France than across the Channel, and second only to Greece within the bloc.

But disliking the EU is not the same as wanting to be rid of it. Since the June 23 Brexit vote, several polls have shown that a majority of French people want to remain in the bloc, and there is no clear majority behind the idea of an In/Out referendum.

Le Pen still has plenty of convincing to do. And Britain now provides a real-life example of what happens when you leave the EU — and in many respects it doesn't look good.

While financial markets calmed down after an initial post-Brexit panic, Britain's economy still faces long-term uncertainty. Bank of England governor Mark Carney warned Tuesday of an imminent economic slowdown.

Just over the horizon, even darker clouds loom — especially if British-based companies lose the right to do business in the rest of the EU.

Then there is the spectacle of Britain's ongoing political crises, with the Conservatives and Labour both in turmoil.

In the best-case scenario, by the time Le Pen is campaigning to be president in earnest next year, Britain will be politically stable but still in limbo with regard to its relationship with the EU.

Not exactly a good advertisement for "Frexit."

"Of course, the British experience is going to be crucial," an aide to Le Pen told POLITICO. "We're hoping that everything goes well, but the rest of Europe will work hard to punish the Brits. Our fingers are crossed for everything to go well."

Stealing from the Front

Six months ago, after losing a regional election battle, Le Pen faced a crucial policy choice.

With the National Front in turmoil, she could choose either to move toward the Right by hardening her stance on social issues and softening the anti-EU rhetoric. Or she could choose to double down on the National Front's core identity: its hatred of the EU.

She chose the latter.

Now, as France's political establishment digests the lessons of Britain's vote, and Catholic conservatives turn against the Front, the choice is making her look vulnerable.

Prior to Brexit, Le Pen enjoyed a measure of exclusivity in being France's Euroskeptic-in-chief. Both mainstream parties, President François Hollande's Socialists and Nicolas Sarkozy's Les Républicains (LR), were equivocal about the EU and avoided advancing hard positions on the bloc's future.

But with Brexit, France has a chance to reassert its role in the bloc, and the mainstream positions have shifted dramatically. All leading candidates for the Right's presidential nomination want to roll back Brussels' powers, give more say to national parliaments and ultimately vote on EU reform in a vast, bloc-wide referendum.

The only difference between that and Le Pen's proposal? They do not want to give the French an option to leave.

"At this rate, the only anti-EU argument left to Le Pen will be her promise to leave" — Jérome Fourquet

Hollande's camp also sounds increasingly Euroskeptic. First Prime Minister Manuel Valls said that France would not ratify the TTIP trade agreement with the U.S., and this week he threatened to stop applying Europe's directive on posted workers.

With those remarks, he stole Le Pen's thunder in denouncing two favorite bugbears of the National Front: free trade and the free movement of workers.

Hours after Valls criticized the posted workers directive, senior Le Pen aide Florian Philippot rushed out a statement challenging the prime minister to follow up his words with deeds. But it had less bite than his usual accusations of collusion with EU overlords.

"At this rate, the only anti-EU argument left to Le Pen will be her promise to leave," said Fourquet of Ifop.

No friends, no Frexit

For Fourquet and other pollsters, Le Pen's potential at the polls currently maxes out at around 30-35 percent of the electorate. In order to reach the magical threshold of 50.1 percent, she needs to widen the party's appeal far beyond its current preserve of largely blue-collar, young, non-urban voters.

One way to earn their respect is to recruit notable conservatives. Former UKIP leader Nigel Farage used the technique successfully against Prime Minister David Cameron, stealing MPs and voters until he left Cameron no choice but to propose a referendum on EU membership.

Yet, whether by choice or by design, Le Pen has not engaged significantly with France's conservative establishment. The National Front has not lured a single conservative MP, and the few transplants it has recruited have been low-ranking and facing dead-end careers.

The result is that Le Pen, unlike Farage, has failed to infect the establishment party with her ideas.

Instead, its politicians have become inoculated to her worldview — and developed antibodies to use against her.

"The French Right is more Euroskeptic, less friendly on immigration, maybe even a bit populist — but it's not about to explode," said Fourquet.

"For Le Pen, that's a problem, because one still cannot win a presidential election without allies in France."