Roberto Unger, descended from a famous Brazilian family, is a respected philosopher, a famous political activist, and a professor at the Harvard Law School (tenured there, thirty-six years ago, at the unusually young age of twenty-nine). He has many just grounds for being famous. But he is best known now, in recent news items, for having taught Barack Obama two courses at Harvard. The professor has released a special video saying that he is too principled to have any further dealings with his former student. His message is that “Obama must be defeated” for failing to advance the progressive agenda.

I freely admit that Unger’s principles are better than Obama’s, that next to him Obama’s credentials as a progressive are muddied and blunted. If I had to choose between them as men of probity, I would prefer Unger as quick as the eye can blink. But in politics we never choose men of much probity. One of the recurring comedies of American politics is the rapture with which people elect a shining prince, and then collapse into self-pitying cries of betrayal when the shine comes off once the candidate is in office. A refrain of dismay runs the fairy tale in reverse: “We elected a prince and he turned into a frog.”

Obama was never a prince. None of them are. The mistake behind all this is a misguided high-mindedness that boasts, “I vote for the man, not the party.” This momentarily lifts the hot-air balloon of self-esteem by divorcing the speaker from political taintedness and compromise. But the man being voted for, no matter what he says, dances with the party that brought him, dependent on its support, resources, and clientele. That is why one should always vote on the party, instead of the candidate. The party has some continuity of commitment, no matter how compromised. What you are really voting for is the party’s constituency. That will determine priorities when it comes to appointments, legislative pressure, and things like nominating Supreme Court justices.

To vote for a Democrat means, now, to vote for the party’s influential members—for unions (including public unions of teachers, firemen, and policemen), for black and Latino minorities, for independent women. These will none of them get their way, exactly; but they will get more of a hearing and attention—“pandering,” if you want to call it that—than they would get in a Republican administration.

To vote for a Republican means, now, to vote for a plutocracy that depends for its support on anti-government forces like the tea party, Southern racists, religious fanatics, and war investors in the military-industrial complex. It does no good to say that “Romney is a good man, not a racist.” That may be true, but he needs a racist South as part of his essential support. And the price they will demand of him comes down to things like Supreme Court appointments. (The Republicans have been more realistic than the Democrats in seeing that presidential elections are really for control of the courts.)

The independents, too ignorant or inexperienced to recognize these basic facts, are the people most susceptible to lying flattery. They are called the good folk too inner-directed to follow a party line or run with the herd. They are like the idealistic imperialists “with clean hands” in Graham Greene’s The Quiet American—they should wear leper bells to warn people of their vicinity.

The etherialists who are too good to stoop toward the “lesser evil” of politics—as if there were ever anything better than the lesser evil there—naively assume that if they just bring down the current system, or one part of it that has disappointed them, they can build a new and better thing of beauty out of the ruins. Of course they never get the tabula rasa on which to draw their ideal schemes. What they normally do is damage the party closest to their professed ideals. Third parties are run by people who make the best the enemy of their own good and bring down that good. Theodore Roosevelt’s’ Bull Moose variant of his own Republican Party drained enough Republican votes to let the Democrat, Woodrow Wilson, win. (His voters, believing he would not “send our boys to war,” saw the prince become a frog in World War I.) George H. W. Bush rightly believes he was sabotaged by the crypto-Republican Ross Perot, who helped Bill Clinton win. Ralph Nader siphoned crucial votes from Al Gore to give us George W. Bush.

All these brave “independents” say that there is not a dime’s worth of difference between the two parties, and claim they can start history over, with candidates suddenly become as good as they are themselves. What they do is give us the worst of evils. If Professor Unger gets his way, and destroys President Obama, he will give us a Romney deeply in political debt to the party he slimily wooed all through the primaries. He will be in a position to turn the Supreme Court from a mainly reactionary body to an almost entirely reactionary one.

Those who think there is no difference between the parties should look at the state that no longer elects any Democrats, the Texas described so well by Gail Collins, with its schools attacking evolution, its religious leaders denying there was ever any separation of church and state, and its cowboy code of justice. If people like Professor Unger, people too highly principled for us folks who muck around in the real world, get their way, they will not give us a prince turned into a frog, but America turned into Texas.