The Democratic presidential race has been defined by Bernie Sanders' prolonged siege of Fortress Clinton. Coming on the heels of Sanders' stunning upset in Tuesday's Michigan primary, Wednesday night's Democratic debate in Miami was no exception.

Sanders technically received the softer questions. But he took them more seriously than Clinton took the hardballs headed her way. So viewers found themselves drawn into a strangely archaic string of controversies about just how radical a form of politics was too radical for a Democrat.

One especially lengthy sequence wrestled with the fallout of American foreign policy in Latin America, including such burning questions as whether Cuba's authoritarian regime deserved credit for encouraging advances in medicine. The matter came to a head when Sanders went out of his way to exclaim, "I'm the only candidate who says no president, not [even] Bernie Sanders, can do it all. You know what we need? A political revolution in this country."

Millions of Democrats seem to agree that nothing short of a political revolution will do in 2016.

For her part, Clinton has insisted that only she — the actual Democrat with the unsurpassed network of allies and influencers — can actually deliver in office on her policy prescriptions. And plenty of Democratic voters are with her — not everyone wants a revolution, after all. Indeed, few Democrats today — remarkably few, in fact — care to invoke recent uprisings like Occupy Wall Street. Certainly Clinton herself harbors few happy memories of 1999's historic Battle in Seattle.

But the rap on Sanders has little to do with the specter of civil unrest and much more to do with the obsolescence or impossibility of a popular political movement for fundamental reform. Doubtless, cynics will point to the dubious impact of the last such movement to make a big deal out of its revolutionary character: Ron Paul's so-called "love revolution." Despite decent press coverage, high novelty value, and a message designed to resonate across party lines, it petered out even before Rand Paul gave up his bid for the White House.

Especially jaded observers might remind us that Barack Obama's own vaunted grassroots network shriveled up and died once his election was in the bag.

Populism can be powerful, but only when it's really popular. And this year, a majority of Democrats just don't want a popularity contest. They want Clinton, no matter how calculated and damage-controlled she is; not because "it's her turn," but because faith is lacking that Sanders could actually govern from the left.

But a worse irony showed through Wednesday night in the swiftly dismissive reaction that Sanders' call for revolution received. The same Clinton enthusiasts who believe Sanders would be crippled as president believe a Trump administration could do anything and everything. While Sanders couldn't get a budget passed, they seem to suggest, Trump could usher in the Fourth Reich. They fear Trump will wreak transformational change on a scale Bernie couldn't even achieve with a decent head of grassroots steam.

Do any subtleties of thought lurk within this hypocrisy? Perhaps Trump is a better negotiator than Sanders, more interested in making great deals that deliver Americans a neo-fascistic surprise. But Sanders enjoys far more institutional support among Democrats than Trump does in the GOP. And while many conservatives want to excommunicate the party bigs who do throw in with Trump, liberals would inwardly smile — if not cheer outright — if established Democrats started endorsing Sanders. At a minimum, Sanders would not have a harder time being president than Trump. And if Sanders had a populist progressive uprising at his back, he would be far more effective than Trump with a cadre of reactionary reformers. Our culture is primed to cede ground whenever the left tries to move the goalposts of justice in the public mind. When the right has tried to do so, they've been portrayed as villains — even before Trump came in the picture.

The conclusion is inescapable: Liberals who think Sanders is copping out as a matter of policy are themselves copping out as a matter of principle. Deep down, they actually prefer a Clinton presidency with no mass enthusiasm behind it. They want the opposite of what Trump voters want: not a risky outsider who can shake up the system, but a canny operator who knows its levers of power like the body of a lover.

But there's just one more irony laying in wait. Clinton is pitching her own kind of insurgent campaign — a sea change from above, not below. Unable to muster the kind of popular excitement that Bill and Barack revel in, she says she's not "a natural politician."

Clinton's refusal to call herself a natural is a sign of just how deeply political she is. And sustaining her elite-centric model of political change in such populist times would be the ultimate chastening for grassroots progressives who thought they had cornered the market on revolution.