George Higgins Moses (1869-1944), a senator from New Hampshire, spoke at a Washington dinner of New England manufacturers in November 1929 and described some insurgent Republican senators as “sons of the wild jackass.” Moses was thinking of the Biblical “wild asses in the desert” in Job 24:5.
 
“Sons of the wild jackass” is rarely used today, but has occasionally described progressive Democrats and Republicans.
 
     
Wikipedia: George H. Moses
George Higgins Moses (February 9, 1869 – December 20, 1944) was a U.S. diplomat and political figure.
 
He graduated from Phillips Exeter Academy in 1887 and Dartmouth College with the class of 1890.
 
Moses was appointed the United States Minister to Greece from 1909-1912. He was elected as a United States Senator from New Hampshire from 1918 to 1933 and served as President pro tempore of the Senate from 1925 to 1933.
 
9 November 1929, New York (NY) Times, “Spurt in Senate Speeds Tariff Bill,” pg. 10:
The attacks on Arnold and Grundy as well as upon Senator Moses for speaking of coalitionists as “sons of the Wild Jackass” at a dinner last night, prefaced five or six hours of consistent work during which the Senate almost went through the metal schedule.
 
10 November 1929, New York (NY) Times, pg. 14:
MOSES STICKS TO TERM.
Says, in Chicago, It Was “Sons of the Wild Jackass.”
CHICAGO, Nov. 9.—Senator George H. Moses of New Hampshire, who arrived here today, sticks to the epithet, “sons o the wild jackass” as the best he can find to describe the insurgent Republican Senators who, in coalition with the Democrats, are dominating tariff making.
 
Senator Moses said that Senator Burton K. Wheeler, Democrat, of Montana, did not quote him in the Senate yesterday with the exactitude that should be an attribute of real scholarship.
 
“Wheeler said I called them ‘sons of wild jackasses,’” commented Senator Moses, “and said I was throwing aspersions on their ancestors. What I actually called them was ‘sons of the wild jackass.’”
 
Google News Archive
17 February 1930, The Spokesman-Review (Spokane, WA), pg. 4, col. 2:
The Wild Jackass Again.
The Minnesota gentleman who has organized the “Sons of the Wild Jackasses club” announces that the purpose of the club is to “bray for fair treatment for the farmer.” He also says the club wishes to thank Senator Moses for supplying it with so lively a name.
 
He could give credit to an even more distinguished source. If memory serves, Senator Moses got his phrase from scripture, and it was not “sons of wild jackasses,” but “sons of the wild jackass.” In this respect the senator was pretty generally misquoted, but he did not complain, as either variation conveys the idea.
   
11 December 1931, New York (NY) Times, pg. 26:
PRICE OF A JOKE.
Behold, how great a matter a little fire kindleth. In November, 1929, Senator MOSES, at a Washington dinner of New England manufacturers, was pleased to refer to the Insurgent Senators as “sons of wild jackasses: or “sons of the wild jackass.” There are varient readings of a text which has rankled in Progressive bosoms ever since. Adopting a suggestion of THE TIMES, he explained that he meant the biblical “sons of the wild ass,” using Hemippus as the type of freedom and independence. But his plea of mitigation didn’t serve. He had made the most successful and famous of his jokes, He ought to be willing to pay the price of it.
 
OCLC WorldCat record
Sons of the wild jackass,
Author: Ray Thomas Tucker; Frederick Reuben Barkley
Publisher: Boston, L.C. Page & Co. [©1932]
Edition/Format:  Book : English
   
21 December 1944, New York (NY) Times, “George H. Moses, 75, Ex-Senator, Dead,” pg. 21:
When he was chairman of the Republican Senatorial Campaign Committee after the Hoover election he referred to the insurgent Southern and Western Senators as “sons of the wild jackass.” The party almost split, but Senator Moses did not recant.
   
Google Books
American Political Terms:
An historical dictionary
By Hans Sperber and Travis Trittschuh
Detroit, MI: Wayne State University Press
1962
Pg. 416:
sons of the wild jackass. A nickname for the independents.
A. Of the several places in which the Bible mentions wild asses, Job 24:5 is probably the one that is behind the use of the term in American politics:
Behold, as wild asses in the desert, go they forth to their work; rising betimes for a prey; the wilderness yieldeth food to them and for their children.
 
B. In a letter of John Hay to Thedore Roosevelt in 1890, we find:
Roosevelt Autobio. 266. You have already shown that a man may be absolutely honest and yet practical; a reformer by instinct and a wise politician; brave, bold, and uncompromising, and yet not a wild ass of the desert.
   
Google Books
The New Language of Politics:
A dictionary of catchwords, slogans, and political usage
By William Safire
New York, NY: Collier Books
1972
Pg. ?:
SONS OF THE WILD JACKASS political irregulars inclined to vote against the party line, especially liberal Republicans; also, reformers in general. John Hay, later Secretary of State, used “wild ass” in the sense of “unreasonable reformer” in an 1890 letter to Theodore Roosevelt: “You have already shown that a man may be absolutely honest and yet practical; a reformer by instinct and a wise politician; brave, bold, and uncompromising, and yet not a wild ass of the desert.”
 
The Congress Dictionary:
The ways and meanings of Capitol Hill
By Paul Dickson and Paul Clancy
New York, NY: John Wiley
1993
Pg. 323:
sons of the wild jackass Midwesterners who came to Congress in the 1920s with a platform combining leftist economics and isolationism. In his 1975 book Conservative Votes, Lberal Victories, Patrick Buchanan resurrected the phrase in describing one of Sen. George McGovern’s speeches. Buchanan, a tough-talking conservative who ran for president in 1992, occupies the opposite end of the political spectrum.