President Obama's statement, delivered moments after St. Louis County Prosecutor Bob McCulloch rendered the grand jury's verdict, was a plea for calm. It was steady and evenhanded. Obama recognized the fear and anger of both sides. He called for calm. He argued that the two sides here were, in a sense, one. "Nobody needs good policing more than poor communities with high crime rates," he said. And, in doing, he disappointed many who had hoped to hear something more impassioned, more outraged, from the president:

Oh man Obama. Not ready to hear this. — Ta-Nehisi Coates (@tanehisicoates) November 25, 2014 Obama it's your second term stop trying to 'gotta hear both sides' this — Ayesha A. Siddiqi (@pushinghoops) November 25, 2014 I respect Obama but his statement tonight is incredibly disappointing. Weak. — Roxane Gay (@rgay) November 25, 2014 Tension here is Obama cannot meaningfully critique a system he temporarily rests at the top of — Adam Serwer (@AdamSerwer) November 25, 2014

The statement — and the reaction — were a precise echo of the first time Obama spoke on Ferguson. Those remarks, delivered on August 18, began with the words "I also want to address the situation in Ferguson. Earlier this afternoon I spoke with Governor Nixon..." and didn't get much more passionate from there. There, too, many of Obama's supporters were disappointed:

Again, I know that President Obama isn't Malcolm X and that he can't say everything that's on his mind, there's just something missing. — Shaun King (@ShaunKing) August 18, 2014 @rembert Feel like he is utterly exhausted. Actually feel bad for him. Not sarcastic pity. Like really feel bad. — Ta-Nehisi Coates (@tanehisicoates) August 18, 2014 Barack Obama is either very tired, doesn’t believe a single word he’s saying re: Michael Brown, or both. — Jamelle Bouie (@jbouie) August 18, 2014 He does know he’s not running for a third term, right? — Saeed Jones (@theferocity) August 18, 2014

As I wrote after those remarks, Obama's supporters aren't asking for anything Obama can't do — or even anything he hasn't done before. Obama was elected president because he seemed, alone among American politicians, to be able to bridge the deep divides in American politics. The speech that rocketed him into national life was about bridging the red-blue divide. The speech that sealed his nomination was about bridging the racial divide. That speech, born of a crisis that could have ended Obama's presidential campaign, is remembered by both his supporters and even many of his detractors as his finest moment. That was the speech where Obama seemed capable of something different, something more, than other politicians. In the White House, it's simply called "the Race Speech." And though the administration often fields demands to repeat it, they have no plans to do so.

The problem is the White House no longer believes Obama can bridge those divides. They believe — with good reason — that he widens them. They learned this early in his presidency, when Obama said that the police had "acted stupidly" when they arrested Harvard University professor Skip Gates on the porch of his own home. The backlash was fierce. To defuse it, Obama ended up inviting both Gates and his arresting officer for a "beer summit" at the White House.

Nor is Obama able to bridge the red-blue divide anymore. Presidents are polarizing figures, and Obama is more of a polarizing president than most.

Moreover, Obama's presidency has seen a potent merging of the racial and political divides. It's always been true that views on racial issues drive views on American politics. But as political scientist Michael Tesler has documented, during Obama's presidency, views on American politics have begun driving views on racially charged issues.

Tesler makes the point with two graphs, one showing that prior to Obama, racially charged controversies didn't tend to split Republicans and Democrats:

And the second showing that since Obama's election, racially charged controversies have begun to sharply split Republicans and Democrats. Note, in particular, the massive divide on the Zimmerman verdict, which came after Obama, speaking in unusually personal terms, said, "Trayvon Martin could have been me 35 years ago":

This all speaks to a point that the White House never forgets: President Obama's speeches polarize in a way candidate Obama's didn't. Obama's supporters often want to see their president "leading," but the White House knows that when Obama leads, his critics become even less likely to follow. The evidence political scientists have gathered documenting this dynamic is overwhelming, and Frances Lee lays it out well here:

If Obama's speeches often aren't as dramatic as they used to be, this is why: the White House believes a presidential speech on a politically charged topic is as likely to make things worse as to make things better. It is as likely to infuriate conservatives as it is to inspire liberals. And in a country riven by political and racial polarization, widening those divides can take hard problems and make them impossible problems.

There are times when that isn't true. There are fights where Obama wants to mobilize his base — and he doesn't much care if it angers his critics. Mere days ago, Obama gave a primetime speech announcing his executive action on immigration. The address was powerful, personal, impassioned. At times, the president seemed close to choking up.

"We are and always will be a nation of immigrants," the president said. "We were strangers once, too. And whether our forebears were strangers who crossed the Atlantic, or the Pacific, or the Rio Grande, we are here only because this country welcomed them in, and taught them that to be an American is about something more than what we look like, or what our last names are, or how we worship. What makes us Americans is our shared commitment to an ideal -- that all of us are created equal, and all of us have the chance to make of our lives what we will."

Obama's supporters were thrilled. His detractors, not so much:

Boehner: "President Obama has cemented his legacy of lawlessness and squandered what little credibility he had left" — Jonathan Strong (@j_strong) November 21, 2014

The polarized reaction wasn't a surprise. But the White House was prepared for it. They were willing to further polarize that debate.

Obama's language didn't soar tonight, just as it didn't soar in his first set of remarks on Ferguson. And that's because Obama can manage polarization on immigration in a way he can't manage polarization on race.

President Obama might still decide to give a major speech about events in Ferguson. But it probably won't be the speech many of his supporters want. When Obama gave the first Race Speech he was a unifying figure trying to win the Democratic nomination. Today he's a divisive figure who needs to govern the whole country. For Obama, the cost of becoming president was sacrificing the unique gift that made him president.