Incumbent presidents generally try to cast their re-election contest as a choice between the imperfect but well-meaning and effective occupant of the White House and the far worse alternative offered by the rival party.
Challengers, on the other hand, try to frame a presidential race as a referendum on the sitting president whose record nearly always contains missteps, or who can be blamed for trouble in the economy or elsewhere.
In short, whether it's the president or the challenger, the way the game is played requires each to define the opposition as well as himself.
And in speeches both President Obama and the likely Republican nominee, Mitt Romney, gave Tuesday, a day that may have been a pivotal day in the 2012 election, both men were hard at work trying to define the other as in one way or another disconnected from the reality of ordinary Americans and from the arc of U.S. history.
Tuesday was probably pivotal because, with Romney's wins in Wisconsin, Maryland and Washington, D.C. primaries, the contest for the GOP presidential nomination really appears to be settled and the general-election campaign begun, according to many analysts.
For his part Obama, in his Tuesday speech to news executives, painted Romney as being in the thrall of the discredited economic notion of trickle-down economics as well as a radical House Republican budget that would eviscerate domestic spending programs that help the middle class in order to give the superwealthy more tax breaks. (Romney spoke to the same news executives' group Wednesday.)
Obama also tried to reinforce the idea that Romney is a very wealthy man lacking the common touch by jabbing the former Massachusetts governor for using the word "marvelous" to describe the House Republican budget. "It's a word you don't often hear generally," Obama said.
Meanwhile Romney, in the victory speech that followed his sweep of the Wisconsin, Maryland and Washington, D.C. primaries, portrayed the president as believing that government knows best.
Romney even went back to the president's days as a community organizer to try and buttress his charge against the president:
"When he was a community organizer and communities were hurt by plant closings, his reaction was to turn to the government for help. He saw free enterprise as the villain and government as the solution."
Romney accused the president of being disconnected from reality because of the bubble that surrounds a president, of "flying around on Air Force One, surrounded by an adoring staff of true believers" which has left the president "out of touch."
While both men worked to define the way they hoped those voters who are in play would see the other party's presidential nominee, they also worked on defining themselves.
In an argument the president has made repeatedly in the past and will make continuously into the future it is he, not his Republican rivals, whose governing philosophy embodies the type of American values that have created the nation that became an economic and military superpower. Worth noting is that he, too, raised his experience as a community organizer though to make a point that was exactly opposite of Romney's attack:
"Keep in mind, I have never been somebody who believes that government can or should try to solve every problem. Some of you know my first job in Chicago was working with a group of Catholic churches that often did more good for the people in their communities than any government program could. In those same communities I saw that no education policy, however well crafted, can take the place of a parent's love and attention.
"As President, I've eliminated dozens of programs that weren't working, and announced over 500 regulatory reforms that will save businesses and taxpayers billions, and put annual domestic spending on a path to become the smallest share of the economy since Dwight Eisenhower held this office — since before I was born. I know that the true engine of job creation in this country is the private sector, not Washington, which is why I've cut taxes for small business owners 17 times over the last three years.
"So I believe deeply that the free market is the greatest force for economic progress in human history. My mother and the grandparents who raised me instilled the values of self-reliance and personal responsibility that remain the cornerstone of the American idea. But I also share the belief of our first Republican President, Abraham Lincoln — a belief that, through government, we should do together what we cannot do as well for ourselves."
Romney attempt at self-definition Tuesday night was as someone seeking to return America to a lost past, as a candidate more in tune than Obama with what made the U.S. the world's indispensable nation in the 20th and early 21st centuries:
"I don't want to transform America. I want to restore to America the economic values of freedom and opportunity and limited government that has made us the powerhouse of the world.
"It's opportunity. It's opportunity, not a check from government — it's opportunity that has always driven America and defined us as Americans. Now I am not naive enough to believe that free enterprise is a solution to all of our problems. But nor am I naive enough to doubt that it is one of the greatest forces for good this world has ever known.
"Free enterprise has done more to lift people out of poverty, to help build a strong middle class, to help educate our kids, and to make our lives better than all the programs of government combined."
In a speech to news media executives Wednesday, Romney went further in defining himself and the president than he did Tuesday evening. Romney offered himself as a successful businessman and former governor who has proven himself as a problem solver.
He described the president, by contrast, as flip flopping on one position after another, taking one stance as president, another as an incumbent seeking re-election.
And he accused Obama of having a "hide and seek campaign", using an example Obama's inadvertently public open-mic comments to Russian President Dmitri Medvedev that after re-election, he would have more flexibility on European missile-defense negotiations.
Now that the Republican primary contest appears to be, once and for all, petering out, the race is on for the president and Romney to see whose definition of the other and himself will most fire up his base while demoralizing the other side and moving those voters who are truly persuadable into his corner.