By Richard Lough and Myriam Rivet
PARIS (Reuters) - The flagbearer of President Emmanuel Macron's European election challenge on Sunday foresaw building a centrist alliance of more than 100 lawmakers, enough she said to thrust the French leader and his grouping into the position of kingmaker in the chamber.
Nathalie Loiseau, a career diplomat whose campaign has faltered after a series of early blunders, said detractors who predicted the president's Renaissance grouping would sit isolated in the European parliament would be proven wrong.
"I'm here to create a centrist group in the European Parliament which makes the difference, a group without which no majority is possible," Loiseau told LCI television.
Representatives from some 10 European parties -- from the Czech Republic and Hungary in central and eastern Europe to Spain and Netherlands in the west -- attended her Saturday rally in Strasbourg, the official seat of the European assembly.
"Those who say that we will be isolated and that will have no clout in the parliament will discover we have at least 100 lawmakers on whom they will have to rely," Loiseau added.
A kingmaker role would give Macron greater influence over shaping EU policy and the filling of key upcoming jobs, such as the European Commission presidency.
An ardent Europhile, Macron wants to redraw the European political landscape, much as he did in France in 2017, building a new political group by tapping into growing disaffection among the mainstream alliances on the left and right.
Polls show the centre-right EPP and centre-left S&D are both unlikely to win a majority. In a sign Macron could count on the support of parties sitting outside the existing centrist group, Portuguese Prime minister Antonio Costa, a Socialist, publicly backed Macron's list of candidates on Sunday.
Created after the last EU elections in 2014, En Marche has no lawmakers in the European chamber but polls show it could win about a fifth of France’s seats in the parliament.
Macron's chief European election strategist, Stephane Sejourne, told Reuters in October it was possible the Renaissance grouping might even dislodge the EPP as the dominant force.
Since then, Macron's authority has been challenged by a grassroots rebellion that has hurt his popularity and forced the president into costly policy concessions. "Yellow vest" protesters took to the streets for a 26th straight weekend on Saturday, albeit in their lowest numbers yet. [nL5N22N0ET]
"For weeks they've been saying that the "Yellow vest" movement is weakening, but the anger is still there," far-right leader Marine Le Pen told BFM TV. Macron had failed to address the protesters' demands for fairer taxes, more spending power and a more participatory democracy, she said.
A Harris Interactive opinion poll this weekend showed Le Pen's far-right Rassemblement National nosing ahead in the campaign race with 22.5 percent of voter support, compared with 22 percent for Macron and his allies.
(Reporting by Richard Lough and Myriam Rivet with additional reporting by Michel Rose; Editing by Toby Chopra)