Lest there be any doubt that Hillary Clinton is a deeply flawed and failed politician — not to mention leader — she has suffered yet another historic rebuke at the hands of voters. In Monday night's Iowa caucuses — a race Clinton once led by some 50 points — she managed to best her democratic socialist competitor by a mere 49.9 percent to 49.5 percent margin. It's the closest race in Iowa Democratic caucus history. Yes, Clinton still won. But this is as weak as wins get. Much of her victory literally hinged on coin flips.

Clinton's weakness in Iowa is hardly an aberration. She has never faced a serious challenge and won. It's hard to think of another elected official as powerful as Clinton for whom that's true.

Why does Clinton keep failing with voters? Rather than a glass ceiling, a vast right-wing conspiracy, or any other phantom menace, it is Clinton who continually hobbles herself. Voters see her as an extraordinarily cynical, power-hungry insider. She is out for herself, not out for Americans. Voters know it.

Bernie Sanders has successfully capitalized on this. His vintage '70s brand of democratic socialism is hardly a slam dunk for a relatively moderate Democratic electorate. But nonetheless, he still offers an instinctive repository of hope for those who firmly rejected Clinton once before, felt gently rejected by the real-life Obama they voted for, and despair at the thought that, this time around, there's really no stopping the machinery of power, Clinton-style.

For many Republicans, that's grounds for a condescending chuckle. The dirty hippies — when will they learn? But in Sanders, and in Sanders' appeal, they face a new kind of phenomenon. Much as the established right failed to grasp how powerful Donald Trump's appeal to combativeness could be, the machine left has completely underestimated the strength and force of Sanders' populist appeal when contrasted with a power-hungry Clinton.

More than any other candidate in recent memory, Sanders has devoted himself to running a "clean" campaign — rooted not only in his basic principles, but even more, in the super principle behind them: the notion that any American can be approached to discuss our destiny in a spirit of friendship and fellow citizenship. While so many political factions, regardless of ideology, have singled out their own special scapegoats — designated scourge classes of scum Americans suitable only for hatred and contempt — Sanders has so far insisted, verbally and nonverbally, on a spirit of forbearance that should counsel and comfort his supporters as much as his opponents. The worst it gets from Sanders is his jeremiad against money in politics.

Contrast that open-palm attitude with Clinton's vision of power — and her consuming hunger for it. Sanders has been a model candidate in refusing to lay Clinton as low as he could on this score. Scummy as Clintonworld may be, Sanders never goes after Clinton for her abject corruption. This is courageous, and smart.

Because more than victory is at stake. National politics will remain a realm of disenchantment and despair until Americans regain trust in the integrity of their would-be champions.

Republicans should take a clue from Sanders — who has far more to teach them about beating Hillary Clinton, and her modus operandi, than they would care to admit. Clinton is a demonstrably weak candidate. She can be beaten. And Bernie Sanders is showing Republicans how to do it.