In presidential politics, should the grading be on a curve? Specifically, assessing President Obama, is it correct to judge his policies on the merits, or in the broader context of legislative realities and the elephant-in-the-room fact of the looming election?

The answer to this question is the difference between a solid B-plus and, on my more charitable days, a gentleman’s C.

The columnist’s instinct — and the columnist’s luxury — is to imagine a more perfect union in which the sustained force of presidential leadership can move a nation. The columnist can choose to dateline her missive from the perfect precincts of Cloud Cuckoo Land.

The politician’s instinct — and the politician’s reality — is to buy himself the chance to do what he wants . . . eventually. He practices the political Hippocratic Oath: First, do no harm to your reelection.

The inevitable clash of these opposing instincts results in frustration and disappointment on the columnist’s part, frustration and fury on the politician’s.

So let’s talk about the “Buffett Rule,” the president’s argument that millionaires should not pay a smaller share of their income in taxes than does the middle class.

From the columnist’s perspective, this is pure political stunt. Not wrong or harmful, just irrelevant. It won’t pass. And even if that happened, it would have a negligible impact on the exploding debt — $4.7 billion a year, or less than four-tenths of 1 percent of this year’s deficit — and take a tiny nibble out of income inequality.

Meanwhile, at what cost? If the Buffett Rule were magically to pass, raising taxes on millionaires alone risks making it harder, not easier, to hit others later. Leading voters to believe that the biggest problem in the tax code is the inequitable treatment of millionaires seems less likely to pave the way for a larger solution than to reinforce the conviction that debt reduction can be achieved pain-free, by taxing the other guy. What shall it profit a president to win reelection but lack a mandate?

So the columnist dusts off trusty presidential quotes, pre-inaugural promises to stop kicking cans down the fiscal road and tell hard truths to a public too long coddled by cowardly politicians.

She imagines the world in which a brave president had embraced the report of his fiscal commission and pressed hard for it a year ago, or in which an even braver president produces a blueprint for fundamental tax reform and campaigns for it now. Or at least doesn’t insult our intelligence by campaigning on something so thoroughly poll-tested and trivial as the Buffett Rule.

From the perspective of the president and his advisers, the columnist is a naive, woolly headed dreamer. What world is she living in? Has she detected any willingness of Republicans to compromise and behave responsibly on taxes, even in an odd-numbered year? Has she seen the Republican budget? Mitt Romney’s plan?

Republicans, they note, are busy denouncing the president as a job-killing tax-hiker for proposing to have a subset of millionaires pay more. What would they do with a real tax reform proposal that limits the mortgage deduction or goes after the tax-free treatment of employer-sponsored health insurance? Do she and her fellow deficit hand-wringers think they’d be happier with Romney in the White House?

I have focused on the Buffett Rule, but this debate is replayed across the spectrum of foreign and domestic issues. Every president confronts this tension, but two things are striking about Obama’s performance.

The first is the degree to which he favors incremental pragmatism over bold experimentation. Sometimes that may be the smart call, and whether this tendency reflects canniness or lack of courage is unknowable. But on the big stuff, you can’t win if you don’t try — or put off trying until after reelection.

The second is the administration’s self-serving effort to wrap political calculus in the sheep’s clothing of good policy. At a White House briefing touting the Buffett Rule, senior officials insisted it was not merely a useful electoral wedge or a reasonable tweak to the code. Rather, they insisted, it was — tah dah! — a crucial baby step toward broader tax reform.

That very day, different administration officials were explaining that the president could not issue an executive order prohibiting federal contractors from discriminating against gays. That move, they argued, would detract from the bigger goal of passing non-discrimination legislation.

Really, guys, I’m willing to mark on a curve. Just not when you act entitled to a perfect grade without it.