The campaign of the French presidential candidate Emmanuel Macron was hit on Friday by a large dump of leaked emails and other documents on a file-sharing website.

Far-right groups in the United States were promoting the leaked information — said to contain both real and fake documents — to cast doubt on the election, pivotal for France and the European Union at large.

Mr. Macron has a roughly 20-point lead over his opponent, Marine Le Pen of the far-right National Front, in the polls.

What We Know About the Breach

The data related to Mr. Macron’s movement, En Marche!, that was leaked on the internet Friday night was dumped hours before a legal prohibition on campaign communications went into effect.