WASHINGTON (CNN) -- Is Sen. John McCain too old to be president?

Listen to some Democrats, and you'll think the 71-year-old Arizona senator is a man lost in a perpetual fog. He is "confused" and has "lost his bearings" or is "out of touch."

Listen to the McCain campaign, and you'll be convinced that Democrats are using those terms to exploit concerns that the presumptive Republican nominee is too old to effectively serve as president.

For his part, McCain tends to answer questions about his age with quips such as, "I'm older than dirt and have more scars than Frankenstein, but I've learned a few things along the way."

The first salvo of the general election's age war may have been launched in May, when Sen. Barack Obama argued in an interview with CNN's Wolf Blitzer that McCain had "lost his bearings" while pursuing the Republican nomination.

The McCain camp claimed that Obama's use of that phrase was "a not particularly clever way of raising John McCain's age as an issue."

Last Wednesday, the issue reemerged when McCain appeared on NBC's "Today" Show and argued, as he has before, that "it's not important" when troops return from Iraq as long as casualties are held to a minimum.

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Sen. John Kerry, an Obama supporter, said in a hastily arranged conference call that McCain is "unbelievably out of touch" and that it "is really becoming more crystal clear... that John McCain simply doesn't understand [the conflict]. He confuses who Iran is training, he confuses what the makeup of al Qaeda is, [and] he confuses the history ... of what has happened between Sunni and Shia."

Susan Rice, one of Obama's top foreign policy advisers, said that McCain had demonstrated a "pattern of confusing the basic facts and reality that pertain to Iraq."

When asked if he was trying to highlight the age issue through his choice of words, Kerry said it was "unfair" and "ridiculous" to make such an assertion. Rice said she was simply highlighting the fact that, in her opinion, McCain has his facts wrong.

For its part, the McCain camp says Obama is the one who is confused.

"Clearly their use of the word 'confusion' had more to do with Barack Obama's complete inability to make sense of his failure to go to Iraq in over 870 days and have a one-on-one meeting with Gen. Petraeus while portraying himself as being informed on the topic," said McCain spokesman Tucker Bounds.

Whether or not the Democrats are playing word games, it is abundantly clear that, for many voters, McCain's age is a real concern.

Roughly one-third of respondents in most recent national polls say that McCain's age could impede his ability to effectively govern the nation.

These percentages are in line with historical trends. Approximately one-third of voters expressed similar concerns about Bob Dole's age in 1996 and Ronald Reagan's age in 1984. (Dole was 73 years old in 1996. Reagan was 73 in 1984.)

The importance of the age question may be magnified this time around because it threatens to sap McCain's support with one of his most critical constituencies: older Americans.

According to the latest CNN/Opinion Research Corp. poll, voters age 65 and older currently support McCain over Obama by 8 points (51 to 43 percent).

Older Americans are a group that, percentagewise, almost always turns out to vote more heavily than the electorate as a whole. McCain will need them firmly in his corner on Election Day.

Unfortunately for McCain, however, older voters also tend to worry more about the age issue than other voters.

"For younger voters, old age is an abstraction," says CNN polling director Keating Holland. "For senior citizens, old age is a reality. In 1996, that difference hurt Dole with senior voters, but didn't seem to matter to voters under 30."

Adding to McCain's age problem is the fact that, due to his war-related injuries, he walks with a stiff gait. Fairly or unfairly, he doesn't always give the appearance of energy and vigor that voters tend to seek in a president.

One of the ways McCain may deal with this image problem is by hiking the Grand Canyon at some point this summer. The senator's wife and campaign aides rarely miss a chance to note that he runs them ragged both on and off the campaign trail.

The senator's use of self-deprecating humor to help put voters at ease is not without precedent. President Reagan famously put the age issue to rest in 1984 by telling voters during a debate with Walter Mondale that, "I am not going to exploit, for political purposes, my opponent's youth and inexperience."

If Mondale ever had a chance of upsetting Reagan in the 1984 campaign, it vanished the moment Reagan delivered that line with devastating effect.

It remains to be seen whether McCain's age will prove to be an insurmountable obstacle for voters this fall. The senator's defenders can certainly point to strong historical precedents of older leaders who served effectively in the past. Winston Churchill was Britain's Prime Minister until he turned 80; Konrad Adenauer served as Chancellor of West Germany until he was 87.

Critics, however, point to Reagan's second term as a possible example of the hazards of age. A number of political commentators questioned Reagan's mental fitness and stamina during his final years in office.

One example McCain certainly doesn't hope to follow: Henry Gassaway Davis. The self-made millionaire and one-time senator from West Virginia earned the distinction of being the oldest American ever to run on a major party's national ticket when he was tapped as the Democratic vice presidential candidate in 1904. The Democrats hoped that Davis, who was 80 at the time, would spend lavishly on their campaign.

He didn't, and in November, his ticket went down to a crushing defeat at the hands of Teddy Roosevelt. Of course, maybe Davis knew that the popular Roosevelt wasn't likely to lose that year, and wisely decided not to throw his money away.

Sometimes, with age comes wisdom.

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