Throughout much of the 20th century Republican and Democratic presidential candidates have repeatedly debated a singular question on the campaign trail: What is the proper role and responsibility of the federal government? In 1980, there was a clamor for smaller, less intrusive government. In the 1930s, Americans expected a bolder, activist profile from their national leaders. And in 2008, this battle has been rejoined with Republicans sounding their quadrennial call for smaller government and Democrats declaring the need for it to play a greater role.

Yet, as Republicans offer an increasingly extreme conservative view of government’s responsibilities, Barack Obama has been given a unique opportunity to chart a new governing philosophy. In his “closing speech” Monday in Canton, Ohio, Mr. Obama did just that offering voters not a vision of “bigger government” or “smaller government,” but instead “better government.” His ability to glide between these two visions of governmental responsibility -- while still remaining true to his conception of activist government -- goes a long way toward explaining his political success over the last 18 months.

For much of the 2008 election cycle, Republicans have described Mr. Obama as the most liberal member of the United States Senate and even worse, as a chronic tax-and-spender. In years past, such attack lines resonated; indeed, for more than 40 years they have been a familiar and effective refrain for national Republicans. The problem this cycle is that Mr. Obama has been difficult to pigeonhole: more a pragmatist than a populist and less a firebrand than a measured politician who doesn’t tilt to political extremes.

Making matters worse for Republicans is that in a year when Americans are concerned about their economic future, government is no longer seen “as part of the problem.” Calls for business regulation are on the rise, polls show that support for the social safety net is at a 20-year high and more than 60 percent of all Americans think government has a responsibility to ensure that every American has health care coverage.

On their own, these numbers suggest that the political pendulum has begun to move in the direction of Democrats. But something else has happened in 2008 to give Democrats a unique political opportunity: Republicans have moved further and further to the right. On the campaign trail, John McCain and Sarah Palin regularly deride any policies that smack of government activism and their description of the roles and responsibilities of the federal government, from a rhetorical standpoint, has become increasingly narrow.

In a speech last weekend in Des Moines, Iowa, Ms. Palin attacked Mr. Obama for his assertion that government should do more to share the wealth. “Under a big government,” she said, “what you thought was yours would really start belonging to somebody else.” According to Ms. Palin, “Barack Obama has an ideological commitment to higher taxes” and a vote for him would lead to government acting like the “other half of our family, making decisions for us.”

But these alarmist statements, which seem directed more to conservatives than swing voters are having an unintentional effect: they are opening the door for Mr. Obama to stake out a more nuanced vision of activist government, one that straddles the middle ground between the political extremes that Ms. Palin is offering.

Consider Mr. Obama’s words from Canton on Monday:

I don’t believe that government can or should try to solve all our problems …. But I do believe that government should do that which we cannot do for ourselves: protect us from harm and provide a decent education for our children, invest in new roads and new science and technology. It should reward drive and innovation and growth in the free market, but it should also make sure businesses live up to their responsibility to create American jobs and look out for American workers and play by the rules of the road. It should ensure a shot at success not only for those with money and power and influence, but for every single American who’s willing to work …. John McCain calls this socialism. I call it opportunity, and there is nothing more American than that.

These words are reminiscent of another Democratic politician who trod the same tightrope between liberal and conservative visions of government: Bill Clinton who in 1996 declared not only that the era of big government was over, but that a “new, smaller government” would “enable all our people to make the most of their own lives with stronger families, more educational opportunity, economic security, safer streets, a cleaner environment in a safer world.”

Like President Clinton in the wake of the Republican shutdown of the federal government in 1995, Mr. Obama has capitalized on the uncompromising arguments of right and left by presenting himself as a conciliator, unifier and most of all a pragmatist who will split the difference of two contrasting visions of government. In his speech at Canton, Mr. Obama offered a repeated “choice” between “allowing our financial system to collapse and spending billions of taxpayer dollars to bail out Wall Street banks;” between tax cuts and no tax cuts; between “a government-run health care system and the unaffordable one we have now;” and between “more money and more reform” on education.

For all of the American people’s antipathy toward “big government” they have never fully embraced the sort of vision that Mr. McCain and Ms. Palin are laying out on the campaign trail; nor have they truly adopted the vision of big government that some liberals hold dear. More often than not the political pendulum has moved from center left to center right, but has rarely strayed too far in one direction or another. This year, it is clearly veering more to the left, but not so far that Americans are ready to return the liberal days of yore: a fact that Mr. Obama seems to understand. His ability to present a vision of activist government that pleases liberals, reassures some skeptical conservatives and directly appeals to independents has been an important, if unexplored, element of his political success and the harbinger of a larger societal change in how Americans view the role of government.