“In some wonky circles,” Salon’s Erik Nelson wrote recently [2], the release of a new Robert Caro volume “is heralded like the Summer of Love release of Sgt. Pepper’s”. This is particularly true in Britain, where the ruling politicians are Old Carovians almost to a man. As volume four, The Passage Of Power, reaches British shelves, it is worth considering just what it is about The Years Of Lyndon Johnson that enchants our leaders so.

While in the US Caro is a favourite of liberals and Democrats – from Barney Frank [3] to Bill Clinton [4] – in the UK Caro is venerated in right-wing policy circles. Michael Gove once read the whole of volume three, Master Of The Senate, while waiting for his wife to give birth [5] (£), while William Hague chose that same volume as his castaway book [6] on Desert Island Discs. George Osborne’s calling of the SNP’s bluff over an independence referendum was attributed by Nicholas Watt [7] to the influence of Caro’s biography, the Chancellor’s “favourite political work”. Throw into the mix Ed Vaizey [8], Mark Hoban [9] and Daniel Hannan [10] – not to mention Michael Howard, who once swapped houses with Caro [11] on holiday – and the biography’s influence is nothing short of remarkable.

It is not enough to rehash the truism that politicians are obsessed with posterity. Of course, this is inescapably a factor: Michael Gove wrote that the biography brings out Johnson’s underlying “tragic greatness” [12] (£), and any politician will sympathise with a reconsideration of a politician vilified during his lifetime.  However, this does not explain the cult behind this particular work. Nor will it work to cite Caro’s exuberant narrative style. Ben Pimlott’s masterly biography of Hugh Dalton [13] is also paced like a thriller – but no politician has chosen it for a desert island.

The biography’s richness and length definitely comes into it. One of the main reasons that Caro’s biography appeals to wonks is that it is, unashamedly, wonkish. Caro’s dissection of political processes is arguably the most extensive ever written outside of academia. Master Of The Senate, the third and most exhaustive volume, dedicates approximately 300 pages to the passage of the 1957 Civil Rights Bill and devotes considerable discussion to arcane legislative procedures such as Senate Rule XXII [14]. What prevents this from being dry is Caro’s flair for drama: he gives a biblical sense of scale to the constitutionality of the filibuster.

Still, this alone will not explain the enthusiasm for the biography among the current governing elite: after all, the entire political establishment relishes esoteric legislative detail. What does mark out Caro addicts Gove, Hague and Osborne is that they are the most staunchly Atlanticist triumvirate of ministers in British parliamentary history. Gove is a self-confessed neoconservative; Osborne is, says Fraser Nelson, a Kissinger obsessive [15]; Wikileaks showed William Hague promising diplomats that the Conservatives would run a “pro-American regime” [16]. All three, significantly, sat on the board [17] of The Atlantic Bridge.

Much of Caro’s appeal to these ministers, we can surmise, boils down to a simple syllogism. The trio are intoxicated by American politics; The Years Of Lyndon Johnson is the most sweeping single work exploring American politics; ergo, the books appeal to their unswerving Atlanticism.

However, allied with this Atlanticism is a vital dimension that completes the picture: morality. Appropriately for their subject – a cowboy hat-wearing Texan rancher – the Johnson volumes have the moral character of a Western. This is particularly true of Caro’s second volume, Means Of Ascent [18], which narrates the primary contest between Johnson and Texas Governor Coke Stevenson for the Democratic Senate nomination. The scheming Johnson is Liberty Valance, while Coke Stevenson, “the living personification of frontier individualism” [19], is Tom Doniphon and Rance Stoddard combined. What’s more, a central Caro theme is that “power reveals” [20]. As the wily Johnson operates power, his latent idealism, on matters such as poverty reduction and civil rights, shines through.

The appeal is obvious to ministers such as Hague and Gove, notable in their moral conception of politics. Gove is evangelical in his rhetoric, speaking often of “moral purpose” [21]; Hague, like Gove, stresses the moral impulse of foreign policy [22] and even wrote a biography [23] of that arch-moralist William Wilberforce. (This does raise the question of why Tony Blair, who personifies these traits, is not a declared Caro lover – but it is perhaps not surprising, as the former Prime Minister was famously indifferent to history [24].)

It is this heady mix of Atlanticism and morality that attracts our present governors to Caro’s biography. American politics has a scale and, at least on paper, an idealism far removed from the omnishambles of British politics: compare The West Wing with The Thick Of It. The Years Of Lyndon Johnson embodies these values in their entirety. However, we would do well to pause for a moment and ask whether our politicians might be reading the wrong Caro book. Whereas the LBJ biography charts Johnson’s transformation from “a devious schemer to a kind of idealist” [25], The Power Broker [26] – Caro’s seminal profile of New York urban planner Robert Moses – charts exactly the opposite: a reforming idealist who turns into a corrupt despot. Politicians, take note.