The derogatory expression lunatic fringe designates a minority group (especially members of a political movement or adherents to a set of beliefs) regarded as eccentric, extremist or fanatical—or simply stupid.
—Synonym: idiot fringe.

The expression lunatic fringe occurs, for example, in The recent election in Spain shows Europe’s right where it’s gone wrong, by Pankaj Mishra, published in West Hawaii Today (Kailua-Kona, Hawaii, USA) of Monday 31^st July 2023:

The state of Britain under a radicalized Tory party should already have been sufficient warning to center-rightists across Europe. The Tories, a once respectable political formation, borrowed generously from lunatic fringe parties such as Nigel Farage’s U.K. Independence Party in hopes of winning over their supporters. The result was Brexit—a calamitous act of national self-harm that won’t and can’t be redeemed for a long time.

But, originally, the expression lunatic fringe denoted—and intended to ridicule—a woman or girl’s hairstyle in which the front is cut straight and square across the forehead.

The earliest occurrences of this expression that I have found are as follows:

1-: From Four Days, a short story by the U.S. author Sophie May (Rebecca Sophia Clarke – 1833-1906), published in Oliver Optic’s Magazine. Our Boys and Girls (Boston, Massachusetts, USA) of February 1874:

“The girls!” exclaimed Miss Lizzie, lifting her eyebrows till they met the “lunatic fringe” of hair which straggled uncurled down her forehead. “The girls!” […]
[…]
“Was that why you studied so hard all winter, and wouldn’t go to singing-school, you sly thing?” said Lizzie, eyebrows and lunatic fringe almost meeting again.

2-: From one of the unconnected paragraphs making up the column Brevities, published in the Lebanon Daily News (Lebanon, Pennsylvania, USA) of Friday 9^th April 1875:

Banged hair is more fitly called “lunatic fringe.”

3-: From the Daily Record of the Times (Wilkes-Barre, Pennsylvania, USA) of Thursday 22^nd July 1875:

“Lunatic Fringe” is the real name given for the fashion which our girls have got up of cropping the hair and letting the ends hang over the forehead. They used to call it “banging,” but “lunatic fringe” is the most appropriate, for it makes a girl look as if Danville, or Harrisburg, contains her proper place of retreat.

4-: From The Daily Evening Express (Lancaster, Pennsylvania, USA) of Saturday 24^th July 1875:

“Lunatic Fringe” is the name given to the fashion of cropping hair and letting the ends hang down over the forehead.

It seems that the expression lunatic fringe was first applied to a minority group by Theodore Roosevelt (1858-1919), 26^th President of the USA (1901-09), in A Layman’s Views of an Art Exhibition, the review of the International Exhibition of Modern Art held in New York City, published in The Outlook (New York City, New York, USA) of Saturday 29^th March 1913:

There was one note entirely absent from the exhibition, and that was the note of the commonplace. There was not a touch of simpering, self-satisfied conventionality anywhere in the exhibition. Any sculptor or painter who had in him something to express and the power of expressing it found the field open to him. He did not have to be afraid because his work was not along ordinary lines. There was no stunting or dwarfing, no requirement that a man whose gift lay in new directions should measure up or down to stereotyped and fossilized standards.
For all of this there can be only hearty praise. But this does not in the least mean that the extremists whose paintings and pictures were represented are entitled to any praise, save, perhaps, that they have helped to break fetters. Probably in any reform movement, any progressive movement, in any field of life, the penalty for avoiding the commonplace is a liability to extravagance. It is vitally necessary to move forward and to shake off the dead hand, often the fossilized dead hand, of the reactionaries; and yet we have to face the fact that there is apt to be a lunatic fringe among the votaries of any forward movement. In this recent art exhibition the lunatic fringe was fully in evidence, especially in the rooms devoted to the Cubists and the Futurists, or Near-Impressionists.

Later in 1913, many U.S. newspapers commented on Theodore Roosevelt’s use of lunatic fringe, thus popularising the expression in American English.

For example, the following two texts implicitly refer to Theodore Roosevelt’s use of lunatic fringe:

1-: From the Binghamton Press and Leader (Binghamton, New York, USA) of Friday 4^th April 1913:

UPLIFTING ART IN CHICAGO

The Illinois “White Slave” commission is investigating the paintings of the Illinois cubists.
Does this mean that paintings will be barred unless their figures are protected by the “lunatic fringe”?

2-: From the column Topics of the Day, by F. H. Young, published in The Evening Bulletin (Providence, Rhode Island, USA) of Wednesday 9^th April 1913:

The strange perversions of mentality with which a large part of the world seems to be afflicted in these days form the dominant and insistent topic of discussion. Do what we will, it is impossible to get the mind diverted from these various eccentricities, chief among which are the doings of the militant ladies abroad and the queer manifestations of the “lunatic fringe” of art.

The earliest American-English use that I have found of lunatic fringe which does not seem to have been inspired by Theodore Roosevelt’s review is from the Greensboro Daily News and Telegram (Greensboro, North Carolina, USA) of Thursday 10^th April 1913:

Mr. Watts has said that he knows no way to distinguish between a reactionary and a progressive; but the course pursued by the reactionary leader in the legislature left little doubt that he did, in point of fact, know the difference. Very early in the session Mr. Watts had progressives like Mr. Wilson, and Governor Craig and Secretary Daniels, placed very definitely in the “lunatic fringe.”

The earliest British-English occurrence that I have found of lunatic fringe applied to a minority group is from the transcript of a speech made by Arthur Lee (1868-1947), Conservative Member of Parliament for Fareham, Hampshire, England, during the  annual dinner of the Fareham Conservative and Unionist Association—transcript published in The Scotsman (Edinburgh, Midlothian, Scotland) of Thursday 5^th February 1914:

“It seems unthinkable to me,” he added, “that any British Government should forego under those circumstances to provide the ships which it has described as essential to our national safety merely in response to the ill-directed clamour of a section. We are continually being placed in a false position merely in order that the lunatic fringe of the Coalition shall be kept from breaking out of the Government ranks. Whilst on ordinary occasions we had no concern whatever with the domestic differences in the Liberal party, we do have in cases where national safety is imperilled.”

The earliest occurrence that I have found of the variant loony fringe applied to a minority group is from The Neosho Times (Neosho, Missouri, USA) of Thursday 30^th August 1923 [erroneously dated Thursday 30^th August 1922]:

Editorials
BYRONIC

Ford of Detroit, ere you start,
Let’s hold converse, hear to heart;
Let me whisper in your ear—
Look well to your steering gear!
Have you filled your gas tank? No!
Fill it full before you go!

Politics, I tell you Hank,
Often gives off odors rank;
Round it there’s a loony fringe
Which I fear will make you scringe.
Your engine cool with H 2 O,
Ford of Detroit, ere you go!

Ford of Detroit, on your own
You will make the race alone,
So I’m telling you, take care,
Look well to your gas, your air,
Watch for punctures! Gosh, I know,
You’ll have troubles if you go!
—B. F.