By Jamie Stiehm
Political commentator, Washington DC
Senator John McCain's personal charms are in danger of turning into a liability as the former Navy fighter pilot looms large in the American sky.
In private the impetuous, nearly manic nature of the Republican running for president is exhilarating - in public it's beginning to look like volatility, a cause for alarm among friends and foes alike.
A grim-faced John McCain at the debate in Oxford, Mississippi
Aside from an unfortunate reference to his opponent as "that one", McCain gave a rather restrained performance on Tuesday in the debate at Nashville, Tennessee.
It was a strategy to show voters he had, as he put it, "a steady hand at the tiller".
But contrast the mellow McCain of Nashville to the warrior of the first debate in Oxford, Mississippi, where he gripped the podium with an expression of suppressed fury, and seemed on the verge of swinging a fist at Democratic candidate Barack Obama.
Viewers could easily draw the conclusion that the candidate is dominated by his passing moods.
When I covered Congress as a reporter years ago, I lunched with the senator and his press secretary in the Senate dining room.
There McCain showed me how he communicated with other prisoners of war in Vietnam, by tapping in Morse code on the table.
Jamie Stiehm is a political journalist based in Washington DC, whose essays on the 2008 presidential campaign have appeared in the liberal, pro-Obama Huffington Post. This is one of a series of comment and opinion pieces that the BBC website will publish before the election.
In a winning way, he also mockingly threatened to thrash author Michael Lewis, who had just cracked my heart. This light-hearted McCain "never met a stranger", as they say.
It's no secret the media had a collective crush on the straight-talking, disarming Republican when he ran for president and lost to George W Bush in 2000. For he was an honourable man, we felt.
One of his finer moments in the Clinton years was reaching out to a junior Democratic senator, Russell Feingold of Wisconsin, to pass a co-authored campaign finance reform bill.
At 72, the snow-topped senator knows this is his last try.
The first sign that his temperament may be "erratic" - as Mr Obama now puts it - was when he cancelled the first night of the National Republican Convention up north in Minnesota for fear of a hurricane down south.
Some thought McCain needed a reason to keep President Bush (who was scheduled to speak) from showing up at the party. But this sort of thing is just not done - it's never happened before.
Then, when McCain suspended his campaign during the financial crisis and headed for the halls of Congress, his move shocked observers on both sides of the party aisle.
He ran the risk of missing the first debate, an odd form of political suicide.
In Oxford, his dark side showed up. Obama, he insisted over and over, does not understand Iraq, Army General David Petraeus and the like.
In fact, McCain has curiously made the "surge" general a personal issue: either you accept his word as gospel and ask to meet him or you don't understand war and peace in the Middle East.
John McCain's choice of Sarah Palin was "spectacularly unpredictable"
(That kind of public deference to a commander, by the way, is counter to the American civil-military code, and points to something deep in McCain's way of seeing the world.)
Casting the unschooled Governor Sarah Palin in an understudy role was McCain's most spectacularly unpredictable decision. Impetuous? You betcha, the woman from Wasilla might say in her downhome way.
The larger picture is that a sobered-up American public wants to look and listen to determine if candidates have clear-cut answers to their questions and worries about a frail economy.
But few know what McCain is going to do next on the national stage, which could make voters uneasy in these troubled times.
The next question: if he does show up, which side of McCain are we going to see?
A minor variation on this theme is McCain's last-minute decision to stand up the popular late-night CBS talk show host, David Letterman - who took umbrage and has not let millions forget the slight.
By his own admission he was a hotheaded young man
Letterman claims McCain told him he had to rush back to Washington, but stayed in New York to be interviewed by Katie Couric, anchor of the CBS Evening News.
Former Ambassador Richard Holbrooke has described McCain's character as molded by the "brawling traditions of the United States Navy". There is something to that.
McCain boasts of his checkered record at the US Naval Academy at Annapolis, Maryland, where he graduated perilously close to the bottom of his class.
By his own admission, he was a hotheaded and privileged young man who narrowly avoided expulsion. Later, as a prisoner of war in Hanoi, the lesson he seems to have learned over long years is to never give up the fight, even when the war is lost.
The son and grandson of admirals, McCain still has a swagger in his step and a permanent air of defiance. It's part of his appeal, but it may sink his ship in this rough political sea.