PARIS (Reuters) - Emmanuel Macron was visibly irritated last March at a news conference ahead of the first round of the presidential election.

FILE PHOTO: French President Emmanuel Macron stands on the steps of the Elysee Palace in Paris, France, June 16, 2017. REUTERS/Christian Hartmann

Having begun the campaign as underdog, but by then already front-runner for the presidency, he was repeatedly asked on morning radio shows how he could possibly govern without a party and a parliament majority.

“I must tell you that I’m astonished to hear some commentators pretend or hope that we won’t be able to have a majority,” he told reporters, before explaining how French presidents had in the past defied the same doubts.

Macron probably had in mind his political history class from Sciences-Po where - like generations of French leaders before him - he was taught about the subtleties of the Fifth Republic’s constitutional system.

The regime was designed by wartime hero Charles de Gaulle, who was anxious that the pre-war parliamentary squabbling he blamed in part for France’s fall to Nazi Germany could not be repeated.

Known as the “fait majoritaire” theory, it is based on a two-round eliminator system for all elections.

Macron was duly elected president via a combination of strong first round support and the backing in the second round of those who did not want a victory for his run-off opponent, the far-right’s Marine Le Pen.

With legislative elections often following the presidentials, the same system has the effect of blocking parties on the edges of the political spectrum, and gives voters an incentive to opt for the sitting president’s candidate.

“From the first round of the presidential election, we entered an implacable, inevitable mechanism which would lead to the triumph of the one who was chosen to defeat Marine Le Pen,” analyst Jerome Sainte-Marie of pollster PollingVox said.

Macron’s rivals did not see that the system could help a party created only a year ago, which had never fielded candidates in a parliamentary election before, and whose leader, at 39, had been unknown to the public three years ago.

But another move by Macron took political experts by surprise and helped amplify his majority on Sunday night to 350 seats or more in the 577 lower house according to projected results. Partial official figures showed he had already reached a majority with 90 seats left to count.

By choosing a young conservative mayor for prime minister, he sowed division and discouragement in an already humiliated Republicans party.

It was the first time a president had chosen a prime minister from outside his political family without being forced to, and the move chimed with French voters’ weariness of the Socialists after a chaotic five years in power.

It also undermined the right’s argument that Macron was just a continuation of unpopular Socialist President Francois Hollande, under whom he had served as economy minister from 2014 to 2016.

Macron repeated the tactic in his ministerial appointments, stealing leading moderates from both The Republicans and the Socialist party.

He also chose not to contest selected seats, including one where Socialist former prime minister Manuel Valls won on Sunday night without the endorsement of his party, thereby driving home divisions in the traditional parties.

However, analysts warn Macron must not let his self-confidence get the better of him.

Macron has said he wants to embody a “Jupiterian” vision of the presidency - whereby the president, very much like the Roman god of gods, speaks rarely except to issue orders.

He has for instance refused to answer journalists’ questions about a minister accused of nepotism.

“The ivory tower effect has always been a danger for the Elysee palace’s occupant,” political analyst Thomas Guénolé of Sciences-Po university. “Most have fallen into the trap.”