If the far-right leader Marine Le Pen pulls off an upset and wins the French presidential race, the formal transition of power will be swift because departing leaders in France do not remain lame ducks for long. But the political upheaval would be significant.
The French Constitution does not set out detailed rules for presidential transitions because the process is mostly determined by tradition, but Ms. Le Pen would have until May 13 to take office — the last day of President Emmanuel Macron’s five-year term.
Newly elected leaders are welcomed at the Élysée Palace in Paris by their predecessors to discuss sensitive information — like nuclear launch codes — before a short ceremony and speech. But the inauguration ceremony is a much smaller affair than in the United States, and does not involve a swearing-in.
The new president is then driven up the Champs-Élysées to the Arc de Triomphe to attend a ceremony honoring fallen service members.
Still, there could be turbulence in the transition if Ms. Le Pen wins, given the potential consequences of such an pronounced lurch to the far right in the heart of Western Europe, and with parliamentary elections coming in two months.
Ms. Le Pen’s anti-NATO and anti-European Union platform could unsettle already-volatile markets as war rages in Ukraine. Her promise to quickly enact an anti-immigrant, nationalist agenda could provoke protests.
Under ordinary circumstances, the current government would resign and the incoming president would name a new prime minister and form a new cabinet, but the presence of Ms. Le Pen means the normal rules might not apply.
Presidents cannot formally dismiss prime ministers, and Jean Castex, who holds the position, has not said what he would do if Ms. Le Pen were to win. He could decide to stay on until the legislative elections in June to at least stall her projects, although Ms. Le Pen could then dissolve the lower house of Parliament to force early elections.
If Mr. Macron is re-elected, Mr. Castex has said he would resign to give his party new impetus before parliamentary elections in June.
Most high-ranking civil servants usually stay on after elections, but at least one official — the head of France’s immigration and integration office — has warned that he would refuse to work under Ms. Le Pen, hinting at potential gridlock in France’s powerful bureaucracy if she were elected.
Her promise to give French citizens priority over foreigners for housing, job and other subsidies would require changes to the French Constitution, but many legal experts say the way she plans to pursue those alterations would be illegal, heralding a potential constitutional showdown.
In June, attention will shift to the parliamentary elections, which are sometimes called the “third round” of the presidential race and will play a crucial role in determining how much leeway the newly elected leader will have to pursue their agenda.
All seats will be up for grabs in the National Assembly, France’s lower and more powerful house of Parliament, in a two-round system of voting. Lawmakers also serve five-year terms.
If the winner of the presidential race, whether Mr. Macron or Ms. Le Pen, is unable to muster a strong parliamentary majority, it could force them into a “cohabitation” — a situation in which the presidency and the National Assembly are on opposing political sides.
That would compel the president to choose a prime minister of a different political persuasion and potentially block much of the presidential agenda.
Jean-Luc Mélenchon, the firebrand leftist who came in third in the first round of the presidential election, has already appealed to French voters to make him that prime minister.