Editor's note: Donna Brazile, a CNN contributor and a Democratic strategist, is vice chairwoman for voter registration and participation at the Democratic National Committee. She is a nationally syndicated columnist, an adjunct professor at Georgetown University and author of "Cooking With Grease: Stirring the Pot in America." She was manager for the Gore-Lieberman presidential campaign in 2000.
(CNN) -- Tonight, President Obama will give a pivotal speech, perhaps the most pivotal speech of his second term. He will address the nation from the Oval Office and make the case for an air attack against Syria.
He is expected to stress that the attack will be limited, a direct response to what the administration has said was the al-Assad regime's use of chemical weapons. He is expected to identify the specific objective and then present the evidence -- some of which has made it to YouTube -- and ask the American people to urge their senators and representatives to authorize the use of force.
The speech will be pivotal not only because it will frame the president's foreign policy on the Middle East but because it will -- or should -- reveal the philosophy behind that policy. Of course, it will have to convince the American people to buy into that philosophy as an agreed-upon expression of American values. He will have to relate this action to things our nation has done in the past and things it hasn't done. In short, he will refer to the "should" and "should not" of history -- our history.
With this speech, the pundits will decide how much political capital the president has left. Given the media's recent track record, that decision will not be based on the content of the speech or even its effect on the debate but on some arcane scoring system. (Of course, some on the right maintained Obama was "running on empty" from the moment he was elected.)
How effective Obama will be during the rest of his term -- how much of his agenda becomes reality -- may well depend on his performance tonight.
Ironically, according to much "conventional wisdom," this is not a speech the president had to give. Under existing law and his authority as commander in chief, he could have ordered the strikes. In fact, had he done so, he might have had more support in Congress, and there would have been less time for opposition to coalesce.
(Still, Secretary of State John Kerry's proposal Monday that Syria turn over its chemical weapons to an international agency is welcome news and once again demonstrates that President Obama and Secretary Kerry are seeking a solution, not an excuse to attack Syria.)
The Oval Office venue for the speech is significant. "The Oval Office invokes the center of the presidential authority. That's the president's office; that's where he supposedly makes decisions, where he governs," says presidential historian Robert Dallek. "The Oval Office symbolizes power."
Indeed, looking through AmericanRhetoric.com's list of the top 100 speeches from the 20th century, of the top 50 since television became the dominant medium, aside from Nixon's resignation,only three were delivered from the Oval Office: Eisenhower's farewell address, Kennedy's Cuban Missile Crisis address and Reagan's "Challenger" disaster address.
Those addresses, and others, indicate why in this case the Oval Office might be the right venue. In each case, the president tied a specific moment or decision not just to the needs of the moment or the reasons for the decision but to the definition of who we are -- and why.
For example, Ike spoke of balance: "Good judgment seeks balance and progress. Lack of it eventually finds imbalance and frustration." JFK spoke of courage: "Our goal is not the victory of might but the vindication of right, not peace at the expense of freedom but both peace and freedom." Reagan spoke of challenge and discovery: "They had a hunger to explore the universe and discover its truths."
We might do well to reread them, for in addressing the need of a moment, they defined our character.
So, yes, it may seem a "risky" venue in which to give a "defining moment" speech. But David Kusnet, chief speechwriter for former President Clinton, says "Oval Office addresses are much better suited to reporting on what is being done than advocating for what should be done. If President Obama can report that progress is being made, an Oval Office address is a good venue for such an announcement."
And we should note this about Barack Obama, in any case: His career has been one understated high risk.
He ran for president as a freshman senator against a well-established and deserving opponent; he confronted the "big question" of race in one of the great game-changer speeches (JFK, anyone?). He reversed the economic freefall, pulling us out of the Great Recession. He staked his presidency on health care reform and achieved something every president tried to do for half a century. (FDR!?)
And all this against not a reasoned opposition but one of rabid hostility.
Obama has a task: Yes, he must justify military action. But since World War I, perhaps the one unforgivable act has been the use of chemical weapons. Civilized humanity has banned them, even in combat, certainly against civilians, especially children in your own country.
Convince the public that al-Assad masterminded the attack, and Congress will authorize.
But Obama should do more. He should challenge us to have the courage to ask: What are the limits of indifference? And he should say, let our judgment match our humanity.
The opinions expressed in this commentary are solely those of Donna Brazile.