Etymology /history of political sense of mandate
TL;DR
The idea behind the political sense of mandate arose from the works of the French philosopher Rousseau in the mid-18th century, and was captured in the neat package mandats impératifs by the leaders of the French Revolution.
The French term was borrowed into English, and the first known appearance is in a late 18th century atlas, by an American, Jedidiah Morse. The term was eventually abbreviated to simply mandate.
Nothing in the history of the term tells us, nor can it, what an appropriate threshold is for calling something a "popular mandate". That's not a question which can be answered with etymology.
Established etymology of English mandate
For etymologies, one convenient place to start is Etymonline, which gives 1796 as the origin of the political meaning you aim at:
mandate (n.)
"judicial or legal order," c. 1500, from Middle French mandat (15c.) and directly from Latin mandatum "commission, command, order," noun use of neuter past participle of mandare "to order, commit to one's charge," literally "to give into one's hand," probably from manus "hand" (from PIE root *man- (2) "hand") + dare "to give" (from PIE root *do- "to give"). Political sense of "approval supposedly conferred by voters to the policies or slogans advocated by winners of an election" is from 1796. League of Nations sense is from 1919.
Unfortunately, it doesn't explicitly mention the 1796 source, but given that the OED is one of Etymonline's principal sources and is also the leading authority on English etymologies, we may turn there.
Here is the OED's entry for mandate in the political sense (paywalled):
- Polit. [After French mandat (1789 in this sense). In quot. 1796 the phrase mandate instructions is probably after French mandats impératifs (1789).] The commission to rule or to pursue stated policies conferred by electors on their elected representatives; support for a policy or measure of an elected party regarded as deriving from the preferences expressed by the votes of the electorate. Also in extended use.
doctor's mandate: see doctor n.[1796 J. Morse Amer. Universal Geogr. (new ed.) II. 375 [France] The members of the legislative body are not the representatives of the department which has chosen them, but of the whole nation, and no mandate instructions can be given them.]
First known use in English
In turn, that work, The American universal geography, or, A view of the present state of all the empires, kingdoms, states, and republics in the known world, : and of the United States of America in particular ... ; illustrated with twenty-eight maps and charts by Jedidiah Morse, published 1796 is available in the Open Library and can be read online. It can also be searched, textually, in Google Books.
Personally, I've searched several online editions both textually and by the given page number (375), but I can not find the actual language quoted by the OED. The only other references I've found to this specific language are quotations of the OED's etymology.
However, I did find an passage in a different work, Memorial of M. Carnot, Lieutenant General of the French Army ... addressed to His Most Christian Majesty, Lous XVIII, 2nd Edition, translated from the French manuscript copies by Lewis Goldsmith, published by T. Hookham Jun & Co, July 1814:
You have received a tacit but imperative mandate, not from your respective departments—by no means from any one section of the people—but from the whole collective people; is is their will which makes the law, not yours: the declaration of right has expressly told you so: it tells you that the law is an expression of the general will.
The degree of similarity here to Morse's language makes coincidence doubtful. This postdates Amer. Universal Geogr. by 18 years, but both works had several editions, and Memorial was written in French before it was published in English, so which way information flowed, or if the phrasing came from a common source, is unclear.
So that's the end of the road so far as the established English etymology.
French mandats impératifs
Turning now to the French mandat and mandats impératifs on which the OED says English's political mandate was styled, we need to find the the 1789 citation. Given the anemic reference, the OED is assuming everyone will know the reference, and therefore it must be quite famous.
So we turn to le Trésor de la langue française informatisé (The Digitized Treasury of the French Language) [via Wiktionary], where we find the relevant political sense:
b) Mandat impératif. Mode de représentation politique selon lequel l'élu doit se conformer aux directives de ses électeurs qui peuvent le révoquer. En droit public français, le mandat impératif est prohibé (Cap.1936):
- Vous qui, en dépit des mandats impératifs qui vous disoient de voter par ordre, avez cru néanmoins que des circonstances impérieuses vous autorisoient à les oublier. Robesp., Discours, 1789, p. 89.
Translated via Google:
b) Imperative mandate. The political representation that the elected official must comply with the instructions of his or her electors who may revoke it. In French public law, the imperative mandate is prohibited (Cap 1936):
- You, who, notwithstanding the imperative mandates which told you to vote by order, nevertheless thought that imperative circumstances permitted you to forget them. Robesp., Discours, 1789, p. 89.
Right date, and Robespierre is certainly notorious enough to justify the OED's oblique reference; the Discours de Maximilien Robespierre (1789 October 21) can be read in the original French in Google Books.
The reference is further bolstered by Wikipedia's article on the imperative mandate, which explicitly traces it back to the French Revolution where the concept was mooted by Robespierre and other leaders during the French National Assembly of 1789, resulting in the royalist faction voting to block the imperative mandate as providing too much power to the people (this may be the origin of the prohibition of the mandate mentioned in le Trésor's 1936 reference¹).
The Social Contract
Finally, Robespierre, in turn, justified his opposition to the mandat impératif based on the the philosophy set out by Rousseau in his 1762 opus, Du contrat social.
Quoting A Critical Dictionary of the French Revolution published 1989 September 28 by François Furet (Editor), Mona Ozouf (Editor), Arthur Goldhammer (Translator), p. 835:
The views of the Jacobin leaders were closer to those of Rousseau. Robespierre cited Rousseau several times in his speeches....
In August 1791, during the Assembly's debates on the revision of the Constitution, Robespierre invoked Rousseau and the Social Contract..
Rousseau's position in that work was, to quote Wikipedia:
Rousseau believed that liberty was possible only where there was direct rule by the people as a whole in lawmaking, where popular sovereignty was indivisible and inalienable. But he also maintained that the people often did not know their "real will", and that a proper society would not occur until a great leader ("the Legislator") arose to change the values and customs of the people, likely through the strategic use of religion.
Thus it must have been Rousseau (and his intellectual predecessors²) where the modern notion of mandats impératifs, hence mandat, hence English mandate was born.
What constitutes a political mandate?
So mandate comes to English from the French Revolution via an American geographer. So what does that tell us about what constitutes sufficient popular will for a mandate?
Nothing. Etymology is not how such things are established.
The Etymological Fallacy
Just because a word meant something in 1762 does not establish what it means today. This erroneous mode of thinking is known as the etymological fallacy, and leads to no end of trouble, and would be particularly pernicious in law.
For example, in c. 1300, girl meant child of either sex (so what today we call a boy would then have been called a girl).
Similarly, if we turn the clock back to Rousseau in 1762, he thought a mandate arose from the will of the whole people. All of them. But he also thought they didn't know what their will was and they needed a sovereign to decide what's best for them, without the distraction of their input.
In turn, Robespierre, the man who earned the sobriquet the Butcher of the Revolution, alternatively urged and opposed the concept as it suited his political needs³.
So is this, then, the authority on which you'd like to found the modern conception of a popular mandate?
That was tried before. It didn't work out so well. Vive la révolution!
¹ Interestingly, by contrast, the imperative mandate, in a slightly different form, is codified in Ukrainian law.
² As well as his intellectual opponents. In particular, Burke. This might satisfy your search for a British perspective on what a mandate should be. Australia's Parliament, in its outline of that country's current debate on mandate, cites the OED's reference of Morse and labels it decidedly Burkean. Burke, of course, being as famous for his support of the American Revolution as for his caustic criticism of the French Revolution and its leaders.
³ I'm going to quote the entire passage from A Critical Dictionary on Robespierre's fickle and opportunistic position of a political mandate, because it's so worth reading:
The views of the Jacobin leaders were closer to those of Rousseau. Robespierre cited Rousseau several times in his speeches. Like the sans-culottes, he, too, rejected the theory of the strict mandate, but he used Rousseau to demonstrate to the people's representatives that their will must not differ from that of the people.
In reality, however, Robespierre's views were dictated by political opportunism. In the fall of 1789 he, like Sieyes, opposed the notation of invoking the will of the people over the heads of its representatives. At that time such a procedure would have strengthened the king's hand.
In August 1791, during the Assembly's debates on the revision of the Constitution, Robespierre invoked Rousseau at the Social Contract in opposition to Thouret, who argued that the people had no means to exercise its power except by delegation.
At that point, the tactical necessity was to combat the Feuillants. In the spring of 1975, at the height of the struggl between the Girodins and the Montagnards, Robespierre again referred to Rousseau's theory of representation, His aim then was to use popular government to crush the Girondin opposition.
A few weeks later, however, however, after the defeat of the Girondins, Robespierre was once more championing representative government: "The people *en masse* cannot govern itself ... all the people could demand was that the Convention march in step with the Revolution. It is now doing so." In February 1794, having put down the popular movement, Robespierre declated "Democracy is not a state in which the people, meeting in continuous assembly, settles all public business on its own."
In other words, Robespierre invoked Rousseauist mistrust of representative government whenever the Assembly seemed to him to be out of step with the Revolution. When it was in step, and when the right people were in power, his Rousseauism vanished and his emphasis on the need for representative government returned.