Inside, "the candidate", or "Johnny Mac", as he is known to his staff, is deep into what has become his trademark activity so far as America's political insiders are concerned: pleasing the media.
Mr McCain, as the rest of America is starting to learn, is running for President, and running, in his case, is the operative word. The outspoken Senator for Arizona already has two morning engagements behind him and is spending, with transparent good will, a full two hours with reporters aboard his comfortably appointed campaign vehicle, the "Straight Talk Express" He is chatting and joking and explaining his policies over doughtnuts and coffee.
Today, "the candidate" inadvertently "leaks" the news that he is suddenly doing rather well. The vast lead built up by the favourite for the Republican nomination, George W. Bush, is on the wane, and that is true, too, in South Carolina, where the third Republican primary election will be held in just over two months' time. Mr McCain, whose military career and heroism as a prisoner of war in Vietnam makes him a strong contender in a state like South Carolina with a large number of military veterans and a concentration of bases, had been trailing Mr Bush by more than 40 points (15 to Mr Bush's 62) as recently as one month ago. Now, according to internal campaign polls he is "well out of his teens".
He is doing far better, too, on the financial front.The amount he has raised over the Internet is nudging $1m (pounds 0.6m) second only to the sum raised the new-tech way by the Democratic challenger, Bill Bradley.
The money raised overall could reach $20m by the end of the year, after a strong surge in the past month. That sum, as his campaign team points out, is comparable with the amount raised by Republican Party front-runners in the past. It only looks meagre against the gargantuan $70m raised by Mr Bush. But, as these self-styled "whacky insurgents" insist, there comes a point where enough money is enough.
"The American voters cannot be bought," says his chief campaign sponsor in South Carolina, Richard Quinn, perhaps hopefully.
At each of his appearances, Mr McCain has one overriding message: the need to reform the current - as he sees it, corrupt - system of political funding, and he presents this as the essential "gateway" to every other change he would aim to introduce as President.
Now, it is physical stamina as much as message that counts, and Mr McCain's schedule is as demanding as any. Perhaps this is why his impromptu discussions with reporters are such a success: they are equally exhausted.
The timetable for his day and a half swing through South Carolina was typical. Before starting Mr McCain managed six hours' sleep.
But the previous night was worse, he arrived in the port city of Charleston at 2.30am, direct from the previous evening's televised debate in the mid-Western state of Iowa. On Tuesday, he addressed a lunch with a rapturous group of Rotarians. It was, they said, the biggest turnout for any Rotarian lunch in South Carolina; bigger even than the lunch with George W. Bush last month.
Mr McCain spoke about reforming the health system without putting the federal authorities in charge. He muffed some of his lines, perhaps the effect of his late night, but the audience did not mind.
He solicited questions, answering flawlessly from education to gun control, on to military preparedness and religion in schools, gays in the military and the handover of Panama (where he happened to be born), he managed to be spontaneous and considered.
Next stop, after a half hour with the press, is Columbia, two hours' drive away inland.
Two fund-raising dinners, one with three comrades from his prisoner-of- war days, were rounded off with more than an hour in a question session on the Internet arranged by the women's Web service, iVillage.
More than 1,000 questions were submitted, from every state of the Union, except, to his mystification, North Dakota. "What's wrong with North Dakota," he quipped to the presenter.
He was visibly tired, his eyes, which he rubbed occasionally, reduced almost to slits, but he sat full square, beside the laptop computer in the television offices, answering in measured tones on a myriad topics, with never a political slip. At 8am yesterday a packed audience of predominantly military veterans awaited him at the Flight Deck cafe.
Two hours later, StraightTalk Express drew into the driveway of Converse College in Spartanburg, a charmingly provincial campus, dotted with southern mansions with sweeping verandas.
Another packed audience, another speech (campaign finance reform), more questions, and more answers. Another day in the candidate's run.