President Barack Obama could not single-handedly transform U.S. politics. Many of his young 2008 supporters learned that to their disillusionment, and as he begins his re-election campaign, the president himself seems a more somber candidate who learned by trial the limits to inspirational change. In his first formal campaign speech, delivered Saturday, Obama’s view of what might happen with a robust use of government power was intertwined with the shadow of a Republican Party that has fought every attempt to use that power.

“The last few years, the Republicans who run this Congress have insisted that we go right back to the policies that created this mess,” he said, speaking in Columbus, Ohio. “Now their agenda is on steroids.”

There was a tiny echo of 2008 at the conclusion of his remarks when he said he “still believes” the country is not as divided as its politics, that people were Americans before they were Democrats or Republicans. But as Obama has reason to know, the country is more divided than it was four years ago, the parties and their supporters more polarized, and he will have to be far more persuasive if he hopes to win and then to govern effectively.

The president riffled through his considerable accomplishments, and was withering in his assessment of Mitt Romney’s plans to let prosperity sprinkle slowly from the hands of the rich onto the heads of everyone else. It is vital for Obama to make this contrast, to remind voters how far backward Romney and his party would take the country.

And Obama’s general goals are the right ones: more college degrees, better teachers, growth in manufacturing, investments in clean energy and preservation of gains in health care and women’s rights. But it’s not enough to simply tick through dreams that will die in a divided Congress. The public has seen plenty of that. Obama needs to spend more time convincing dubious and disillusioned voters that he can achieve these goals.

It’s true that he has repeatedly been burned seeking elusive “grand bargains” with Republican leaders who proved unwilling or unable to compromise. But even Democrats say the president has been too aloof in his first term, not bothering to make his case in the Capitol, not interested in the LBJ-style flesh-pressing or arm-twisting that can rescue a law out of the mortuary of bills.

The president can let loose a great speech, but without follow-through Congress can be counted on to muck up the details, as he should have learned from the fight over the health care reform law of 2010. He never made the sale with the public on the law, and the two or three sentences he devoted to it in his speech were insufficient. If not struck down by the Supreme Court, the core of the law will be fully felt in his second term; rather than shy away, it is time to explain to the public in detail what that would mean and why it is important that he be there to fight for it.

Similarly, the speech lacked any detail of his plans to shore up Medicare while reducing its untenable cost growth. If he is going to counter the Republican plans to end Medicare’s guarantee to older Americans, he will have to do better than a quick promise to reduce wasteful spending.

Voters already know that Obama can lift their hopes with a powerful speech. This time around, they will be seeking far more than inspiration.

— The New York Times