About five weeks ago, the psychology professor Drew Westen published a very long and not very persuasive essay in The New York Times arguing that Barack Obama’s presidency has fallen short of his supporters’ expectations because he has failed to tell the right “story” to the American people. Last week, Westen took to CNN.com to defend his argument against several critics, including Jonathan Chait. Characteristically, Chait promptly attacked again.

I don’t have much to add to Chait’s take-downs of Westen—or the rebuttals by other writers—but there is one weak passage in Westen’s CNN piece that Chait declined to address. As part of his argument that his critics incorrectly downplay the potential power of presidential rhetoric, Westen writes:

The “oratory is irrelevant” argument is especially peculiar in the case of Obama, whose soaring oratory is precisely what won him the presidency, particularly in the face of a thin résumé. It would be difficult to argue that candidate Obama would have ever become President Obama had he not delivered his race speech in Philadelphia, which put an end to the Rev. Wright controversy and breathed new life into his campaign.

This argument, which Westen isn’t the first to advance, probably overemphasizes Obama’s impressive campaign oratory at the expense of other factors that contributed to his victory. But accept for the sake of argument the claim that Obama’s rhetorical prowess was essential to his bid for the White House. His speech-making skills on the campaign trail are nonetheless not nearly as relevant to his presidency as Westen would have you believe, because the problem he’s trying to solve with his presidential speeches is very different.

Consider Obama’s situation in late 2007, as his presidential campaign began in earnest. The weakening economy and the failed presidency of George W. Bush made it very likely that the next president would be a Democrat. Meanwhile, the Democratic Party had a clear front-runner who inspired limited enthusiasm, but with whom—with the obvious exception of the Iraq War—Obama had few sharp policy disagreements. So his task was to convince Democratic elites and voters that he was a better standard-bearer for the party than Hillary Clinton was, while also assuring general-election swing voters—who were already inclined by circumstance to support a Democrat—that it was safe to vote for a relatively inexperienced African American with an unusual name.

In short, Obama had to persuade a range of people who were open to being persuaded to adopt a particular understanding of himself, tied to particular understandings of politics, progress, patriotism, etc. (Many of his speeches, especially including the “race speech” in Philadelphia, can be understood this way.) His rivals, of course, were pushing competing understandings as they sought to discredit him. But Obama had the upper hand in that contest—he is, after all, the world’s leading authority on himself. He’s even written an acclaimed book on the subject!

It’s not clear, though, why Obama’s apparent success in that task would make him better equipped than the average president to persuade members of the public, or of Congress, to adopt particular understandings of the political landscape or of public policy. And, contra Westen, the rhetorical power of the presidency in these cases is limited: no matter how many times Ronald Reagan is referred to as the “Great Communicator,” there’s little evidence that presidential speech-making can move public opinion, or congressional votes, on most issues. (For more on this point, plus a discussion of the circumstances in which presidential rhetoric can be effective, see this excellent post by John Sides.) That’s probably because, while the president has the “bully pulpit,” he’s competing with a lot of other voices, and with the pre-existing political convictions of people who disagree with him, some of whom get a vote in Congress. It’s also because, unlike during a presidential election, most people aren’t paying attention to day-by-day governance.

In Westen’s world, the important difference between Obama’s oratory on the campaign trail and in the Oval Office resides with the speaker. A better way to look at it would be to focus on the changes in audience, context, and subject matter. Viewed that way, the apparent paradox—how can Obama’s rhetorical power be limited as president, when it was central to his candidacy?—is no paradox at all.

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Greg Marx is a CJR staff writer. Follow him on Twitter @gregamarx.