“You can’t judge a book by its cover” is a time-honored saying.

We are supposed to look for content and not make judgments based only on appearances.

But when it comes to elections, we often ignore that message and decide on political candidates by relying more on how they appear than on what they say.

President Barack Obama is a prime example of a public official who ignored that fact in the first presidential debate.

He came across low-key, defensive and diffident, especially compared to a confident Mitt Romney. His lead evaporated.

Obama’s failure to dramatize his presidency is nothing new. Just remember the picture of him in the command center when Osama bin Laden was found. Somebody else sat at the head of the table; he was hunched down on a side bench.

Even his television ad refuting Romney’s debate position on taxes shows him bent behind his desk saying he approved the message, when he could have been standing and forcefully saying: “I approve this message and here’s why.”

After the first debate, he said that what Romney did “wasn’t leadership, that’s salesmanship.”

Doesn’t he understand that part of leadership is salesmanship?

President Ronald Reagan, a former pitchman for General Electric, did.

By the second debate, Obama got it. We will soon see if his feisty performance put him on the comeback trail.

Style may matter more than substance in the presidential race.

Scientific American magazine carries a story this month that says voters are “predictably irrational,” often picking a candidate who “looks more competent” or “has the deepest and most resonant voice.”

Presidents now regarded as popular and successful, whatever their failings in office, were people whose style was appealing.

Harry S. Truman was refreshingly plain spoken. John F. Kennedy was articulate and relaxed. Ronald Reagan was confidently self-deprecating and reassuring. Bill Clinton was like your friendly neighbor, the smart one.

They seemed comfortable with themselves and showed an easy, unscripted sense of humor that emerged from their sense of self.

Their success showed that voters valued their strong leadership qualities, perhaps even more than the substance of their policies.

They knew what they were doing and were sure it was right for the country. The key quality that came across from them, but sometimes seems to be lacking in Obama, is an air of self-confidence.

Beyond that, they were able to think on their feet. Faced with a debating challenge, they could come up with strong points to support their positions and attack those of their opponent.

Should we really decide based on how a candidate conducts himself or herself rather than based on accomplishments or proposals?

Political campaigns intentionally depart from the truth so much that voters may find it hard to believe what candidates and parties say. Fact-checking in the media has exploded in recent years mainly because campaigns have come to pay so little attention to the facts.

Many voters now have such a high level of distrust of government and candidates’ proposals that they find it difficult to know what the truth is or to believe campaign promises.

Most voters have made up their minds about whom they support relying on a candidate’s accomplishments, proposals, ideology, or party affiliation. They are committed, and a candidate’s failure to project inner self-confidence may not matter.

The debates don’t change the minds of such voters, though the forums may encourage or discourage them.

Close elections, like we face for the presidency and control of Congress this year, are decided by a small percentage of voters. These voters are undecided until late in the campaign, not having been persuaded by often-repeated campaign promises.

In this year’s close races, the debates have taken on an unusual importance, giving the undecideds the chance to make judgments based on the candidates’ style.

Following the first debate, Romney gained in the national polls. In swing states ”“ those enough in doubt that they will determine the outcome of the presidential election ”“ the move to Romney was even greater.

Clearly, the shift in the presidential race was the result of the debate. While Romney gained, GOP hopes of taking control of the Senate faded.

Now we get to see if the change in Obama’s style matters.

The next two weeks are the period when the undecided make up their minds. Learning more about where the candidates stand may help, but how they perceive of the candidates as leaders will probably matter more.

And in a world where each day provides unanticipated political challenges, a choice reflecting perceptions of how a person conducts himself may make as much sense as deciding based on campaign promises.

— Gordon L. Weil is an author, publisher, consultant, and former official of international organizations and the U.S. and Maine governments.

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