After Michelle Obama’s moving pyrotechnics of Tuesday, and Bill Clinton’s droll evisceration of the Republicans on Wednesday, it would be easy to declare the Democratic Convention a political success. Key goals have been met, powerful themes articulated. Easily, President Barack Obama could reprise those powerful notes, stir the crowd, and head home.

That would be a big mistake. Nobody in this Convention has told the American people what President Obama would try to do in a second term. So far, he hasn’t either. This is his big moment to do so.

Of course, we’re used to thinking that Barack Obama can do no wrong when it comes to giving a big speech. Didn’t he launch his improbable ascent from this very podium in 2004? But Obama’s speeches have been oddly uneven. When he speaks of his own story—and how it fits into the American story—he has been nothing short of astonishing.

He has had a much harder time connecting that narrative to the governmental goals and policy outcomes that are the core of leadership. Time and again, he has chosen not to—or been unable to—use big national platforms to make striking political arguments or powerful rhetorical claims.

At Denver four years ago, his main task was to show a still uneasy public that he was not terribly different from other Democrats. The speech was a success, but only because it managed to meet the standard of predictability. His Inaugural Address, at a time of crisis, was largely a sober discussion about responsibility. In the State of the Union addresses throughout his administration, themes and slogans came and went: "The New Foundation" was briefly tried out for the first time since the Carter administration; then there was Obama’s vision of an economy “built to last.” (The slogan, for its part, clearly was not.)

Can President Obama give a defining issues driven speech? Yes, he can. Every so often, he has powerfully linked policy and values. At Osawatomie, Kansas, last year, he argued for tax and regulatory policy within broad themes of national growth and greatness. It was a bit populist, an artifact of the season of Occupy. But it worked.

The real test for leaders, of course, is what they say when tens of millions of people are watching. But a few months later, when Obama had a national television audience for his State of the Union, his earlier themes vanished. A forensic archeologist would struggle to find a trace of his Kansas speech. Because of his failure of follow-through, that earlier speech effectively didn’t count.

Thursday night will be another chance for President Obama to speak to a truly national audience. So what do I hope we hear?

Policy goals. What his goals are for a second term. What would he do, if he could, to restore robust economic growth? What is his vision of immigration reform? Of an ideal tax code? How—concretely—can we restore the middle class?

Many will wince at the idea that he should deliver a laundry list of initiatives. But the public craves policy. It wants to hear from political leaders what they want to do. It’s impossible to frame a choice between two policy approaches if you won’t say what yours is.

A robust defense of the role of government. For decades, with passion and zest, Republicans have set out their vision of the role of government. (Hint: They don’t like it very much.) That “great debate” has been more of a monologue. Democrats have shied away from defending government’s role. The public distrusts the state but likes specific programs, they have reasoned—so Democratic oratory often has sounded like a string of eloquent poll questions.

But a convention speech is precisely the right time to set out a broad defense of government’s role, and where it stands in relation to the private sector. The greatest ever Democratic convention acceptance speech—Franklin Roosevelt’s in 1936—did just that. Speaking in Philadelphia, he said that just as the Founding Fathers fought political tyranny, the Democrats now were fighting “economic royalists,” and using government to do it.

A focus on democracy. This year the very integrity of American democracy is at risk. Citizens United and other court decisions have given unnerving new power to big campaign money. Earlier this year, we winced at the sight of billionaires sponsoring candidates as if they were race horses. Now the role of big donors has only magnified, increasingly in secret. Voters understand that this new money will lead to corruption on epic scale. We’re in the early days of a major scandal; we just don’t know what it is yet. Add to that the wave of laws, passed by GOP state legislatures, that make it harder to vote. (Fortunately, many of the worst have been blocked or blunted by courts, prosecutors and voters—but not all.)

Pollster Stanley Greenberg has argued powerfully that the public won’t back a progressive vision of government unless it believes that the political system has been reformed. So I hope that President Obama makes the state of our democratic system a major theme of tonight’s talk, too. His advisors may warn him that it will sound like sour grapes, or risk accusations of hypocrisy from the media, given that he is raising funds himself. But public dismay over broken government is a broad concern, not a narrowly partisan one. Anyway, it’s the right thing to do. We can't solve our national problems if we don't fix the system.

Surprise us with optimism. It's a truism that the most optimistic sounding candidate wins. But largely, it's true. He can paint an uplifting picture of a prosperous country with wider opportunity. Let's hear about improvements in American energy, tech, manufacturing, and education.

Mitt Romney gave the Democrats a surprising opportunity. By limiting his own policy pronouncements to a few vague sentences, he gave the incumbent party a chance to define him and his approach. By harkening to an imaginary picket fence past, Romney has set up a contrast with a bold futurist vision. Democrats desperately want this to be a choice between parties, not just a referendum on the Obama presidency. Obama’s speech will convey optimism, confidence, a sense of moving to the future. But if he doesn’t say what he wants to do when we get there, it will be a major missed opportunity—not just for campaigning, but if he wins, for governance.