Of all the critiques made of President Obama’s performance in the first debate, the most telling, I think, was leveled before the debate — 2,000 years before, more or less. The criticism came in the form of a question, but then, that’s how rabbis talk.

“If I am not for myself, who shall be for me?” asked Rabbi Hillel — the first of three questions that he believed people needed to ask themselves if they were to lead decent lives.

Obama’s decline in the polls suggests that Hillel was on to something. In Denver two weeks ago, the president simply did not advocate at all persuasively for himself, his achievements or his positions. It wasn’t for lack of talking points. Thanks in good part to his stimulus, the U.S. economy did not tumble into a depression in 2009 and is moving, albeit haltingly, toward recovery. What’s more, the American Jobs Act that Obama has proposed — and that Republicans have stymied in the Senate and refused to pass in the House — would stem the continued hemorrhage of jobs in state and local governments and shore up both our sagging infrastructure and the underemployed construction sector.

But the president did not mention the Jobs Act in Denver, even though, when placed side by side with Mitt Romney’s pledge to create 12 million jobs though tax cuts and deregulation — the very policies that failed to create jobs during the presidency of George W. Bush — it has the singular virtue of plausibility.

I don’t presume to know why the president wasn’t sufficiently for himself in the first debate — why he didn’t have even a decent closing statement. I do know that he suffers from a fundamental asymmetry between the two campaigns: Romney has an agenda for the next four years, however dangerous (repealing Dodd-Frank, turning Medicare into vouchers) or impossible (cutting taxes, raising military spending and reducing the deficit) it may be. Obama has largely declined to put forth an agenda, presumably on the theory that running against Romney’s platform would have lower risk and higher reward.

Obama’s case would be stronger, however, if augmented with some new proposals. A vote for Obama should mean more than consolidating the reforms of his first term and fending off the Republicans’ dismantling of the New Deal. In Tuesday night’s debate, why not unveil a plan to reinstate the Glass-Steagall barrier between investment banks and federally insured depositor banks? How about putting a ceiling on the level of assets a bank can have, as Sen. Sherrod Brown (D-Ohio) has proposed? These ideas aren’t just prudential economics; they would also align the president with Main Street against Wall Street.

Such an alignment would work to the president’s advantage not only in itself but also because Romney remains a creature of Wall Street, a man comfortable in homes where he can casually slander half of the American people to the quiet approbation of his donors. Which brings us to Hillel’s second question — “If I am only for myself, what am I?” — a query that many Americans would like to pose to the nation’s increasingly decoupled rich citizens, whose stock holdings rise in value while median incomes fall and whose profits increase as wages decline. It’s a question Obama should pose to Romney, who isn’t for himself only, of course, but is surely a tribune for the disconnected 1 percent, championing tax, labor and regulation policies that would benefit them at the expense of the other 99 percent.

Even though the president’s standing in the polls has weakened, public assessment of the candidates’ class orientations has not shifted. Obama still has a huge lead on the question of who is better attuned to middle-class concerns; Romney is still identified as having policies that would disproportionately comfort the already very comfortable. Vice President Biden drove home this point with a sledgehammer in last week’s debate. Obama will never have Biden’s street-corner sass; there is no populism in the president’s DNA. But Romney’s tax proposals and his insistence on repealing financial regulations would so coddle the rich at the expense of the general welfare that Obama should attack them in the name not of class but of the nation. At this stage in the campaign, angering a few more hedge-fund guys will only help the president in Ohio, Florida and Nevada.

Before he takes the stage Tuesday, Obama would do well to recall Hillel’s third question: “If not now, when?” This is the night to stand for himself and those Americans whose lives and fortunes are linked to the real economy, not the world of arbitrage and offshore banks. Tomorrow might be too late.