Ambition is the most consistent, yet variable, component of public life. Lincoln and FDR had it, and that was good. Benedict Arnold and Joseph McCarthy had it, too. And that turned out very bad.

Bernie Sanders is not often described as an ambitious man. But you don’t run for mayor of your city without a dash of ego and drive. You don’t leverage that position into a congressional seat without wanting more. And no one ends up a US senator without the gnawing, often insatiable, hunger peculiar to political ambition.

After more than a quarter century of playing at the margins of the political arena, Sanders has entered the main contest. Running for president is the most public imprint of an individual’s ego, ambition and desire. That’s not to suggest Sanders is in it solely for himself; his ideals have been manifest throughout his career. It’s merely a statement of political fact, as indisputable as weather.

Hillary Clinton’s weather patterns are familiar. “I am not a natural politician,” she said during a debate with Sanders, “in case you haven’t noticed, like my husband or President [Barack] Obama.” Having been eclipsed, in different ways, by two preternaturally gifted politicians, Clinton nevertheless kept plugging. The one-time Goldwater Girl knows her political archetype cold: She is a persevering Nixon forever working to get a leg up on some charming damned Kennedy.

Clinton’s marriage uniquely boosted her. But her diligence and dogged mastery of detail would otherwise be familiar to Nixon. In Six Crises, Nixon wrote: “I won my share of scholarships, and of speaking and debating prizes in school, not because I was smarter but because I worked longer and harder than some of my more gifted colleagues.”

As a law student at Duke University, an upperclassman reassured an anxious Nixon that he had what it took to succeed — the “iron butt” to endure countless hours of study.

Clinton has an iron butt. Sanders doesn’t. He still exhibits difficulty filling in the details of his own proposals. His cursory tour of contemporary global affairs, one year into his surprisingly competitive campaign, ends in a political safe house, and a prescription immune to contradiction: If you travel back in time to 2002, don’t vote for the Iraq war.

A disciplined orator, he has made a marketable virtue of quirky authenticity. But he’s no Kennedy or Obama. And he set a quixotic goal from the outset of his campaign, repeatedly saying that his success depends on fomenting a peaceful “revolution.” That’s a tall order six years into a Republican Thermidor in which reaction, not revolution, has been the most salient feature of American politics. As the Republican primary confirms, the scorching headwinds haven’t cooled. So what compels a 74-year-old to make his first presidential run into the furnace blast?

It seemed at first that Sanders was running mostly to make a point. His hero, American socialist Eugene Debs, ran repeatedly for president in the first two decades of the 20th century, hitting a peak of 6 per cent of the national vote in the four-way election of 1912. Debs didn’t expect to be elected. But he did hope to lead a revolution, and his motivation would be familiar to any Sanders supporter.

Debs was prosecuted in 1918 for making an antiwar speech under the Espionage Act. Addressing the court, he lamented rampant inequality, which enabled 5 per cent of the population to control two-thirds of the nation’s wealth - a ratio that, a century later, is once again familiar. Debs attacked “the plutocratic element that absolutely rules our country. They privately own and control our common necessities. They wear no crowns; they wield no sceptres; they sit upon no thrones; and yet they are our economic masters and political rulers.”

With Sanders, the rhetoric is reprised but the goal seems to be mutating. If Sanders ever thought of himself as a protest or “movement” candidate, he does no longer. If he ran in part because he never had before, and would be too old to ever try again, his trajectory has changed. His revolution has fallen short of capturing even half the Democratic Party, let alone the number of voters powering respective assaults on the castle by Donald Trump and Ted Cruz. But revolution has been displaced by more pragmatic concerns.“I think we have a real shot to end up with more delegates,” he said Sunday on CBS’s “Face the Nation.”

Electoral success, popularity and a spectacular grass-roots fundraising organisation have brought Sanders tantalisingly near the Democratic nomination. He is beginning to taste something for which some doubted he had the appetite.Last week he launched a surprise attack on Clinton, the most prepared Democratic candidate for president at least since Al Gore in 2000, as “unqualified.”

In a campaign that Sanders casts as a contest between his righteous idealism and his opponent’s compromised ambition, his aggressive overreach was clarifying. Clinton’s ambition has been on public exhibit for years, producing volumes of commentary, much of it snide. Sanders, citing a higher calling, has escaped such scrutiny. He may not share his opponent’s ferrous backside, but Sanders knows far more about the metallurgy of ambition than he lets on.

— Bloomberg

Francis Wilkinson writes on politics and domestic policy for Bloomberg View.