PARIS — President Emmanuel Macron, who upended France’s political establishment with his election in May, is breaking ground again, but in an unwelcome way: a rapid and nearly unequaled drop in the polls.

The young president lost 10 points in one month in one poll, eight in another and seven in a third. Not since the first months of Jacques Chirac in the mid-1990s has any president fallen so far so fast.

Mr. Macron, at the head of a fledgling political movement, marked a victory that was always as tenuous as it was momentous. A former investment banker, he bested France’s traditional political parties and fashioned himself as something of a centrist, giving both left and right reason to support him, but also ample room to regard him with suspicion.

Now, it appears that France’s initial romance with the untested outsider to politics may be quickly fading.