On paper, the most important speech of the Republican convention will be delivered by Mitt Romney on Friday, as he accepts the party's presidential nomination.
But the one that could make the most difference of all comes today. And it won't be delivered by a politician - at least not a professional politician.
Under the revised, Isaac-compressed schedule of the convention, Ann Romney will have some prime-time competition in the hefty shape of New Jersey's combative and trenchant Governor Chris Christie.
But Christie is just a politician. Ann Romney has the crucial task that could conceivably decide the election - of making Americans (particularly American women who currently prefer President Barack Obama by a wide margin) to like and trust her husband enough to send him to the White House.
The simple fact is that Ann Romney is a far better campaigner than her husband. Where her husband can appear unearthly, robotic and managerial, untouched by the disasters that plague the lives of ordinary people, Ann Romney comes across as straightforward and natural. In a word, normal.
At 63, she has the qualities of the traditional Republican first lady - not a career woman like Hillary Clinton or Michelle Obama, much more the supportive wife and homemaker in the mode of the two Bush presidential wives, Barbara and Laura. The family is suitably picture perfect too, a handsome husband and five strapping and wholesome sons.
But if Ann Romney wears the coat of privilege, right down to a passion for equestrianism and ownership of Rafalca, a dressage horse that competed in the London Olympics, the reality is more complicated. Ann Romney has had two reported miscarriages, she has overcome breast cancer. She suffers from the incurable and potentially debilitating illness of multiple sclerosis.
All this makes her the ideal "humaniser" of her husband. Some have dubbed her the "Mittigator".
Romney needs help in that vital presidential-preference category, the candidate "you'd most like to have a beer with". As a teetotalling Mormon, he doesn't touch the stuff. But if anyone can help square that circle, it's Ann.
Contrary to appearances, she is a first-generation American, whose father, Edward Davies, emigrated from south Wales to the US in 1929. He became a successful businessman and settled in the wealthy Detroit suburb of Bloomfield Hills. Ann Romney met her future husband in 1965 when she was just 16. The following year she converted to Mormonism and in 1969 they were married. Five children followed.
Nothing, however, prepared her for the day in 1998 when she was diagnosed with MS. "I was pretty desperate, pretty frightened and very, very sick," she told the Associated Press in 2004. But she has managed to keep the symptoms under control with a variety of treatments that include acupuncture and horse riding.
Today though, Ann Romney will be selling her husband to the American people. The Mitt Romney she'll be describing is not the bean-counter at Bain Capital or the competent Governor of Massachusetts but the guy who stood by her when the doctors told her she had MS. "You can count on him," she has said. "He won't abandon you in the hardest times."
She'll be schmaltzy, a little over the top, as is the way with many US political convention speakers. But just possibly, it'll work.
STATE OF RACE
Barack Obama/Joe Biden 46 per cent
Mitt Romney/Paul Ryan 42 per cent
Would be fun to meet 48 per cent
Likeability: 54 per cent
A good person: 47 per cent
More eloquent: 51 per cent
Man of faith 28 per cent
Would be fun to meet 21 per cent
Likeability: 26 per cent
A good person: 29 per cent
More eloquent: 21 per cent
Man of faith 40 per cent
Favourable 49 per cent unfavourable 51 per cent
Favourable 48 per cent unfavourable 52 per cent
Will protect American jobs: Obama 36 per cent, Romney 33 per cent
Economy on the wrong track: 75 per cent
Fuel prices on the wrong track: 83 per cent
Cost of living doing badly: 79 per cent
Obama 46.8 per cent, Romney 45.7 per cent
Electoral College (270 needed)
Obama 221, Romney 181
Obama 55.6 per cent, Romney 43.7 per cent