Emma Thompson plays the Hillary Clinton figure in the film, none too loosely based on the Clintons' journey to power. Lester plays the campaign manager.
In the novel from which the film is adapted, the two have a one-night affair. In the movie which opened the festival last night, although Lester comforts Thompson when she hears of her husband's infidelities, the pair just stare at each other meaningfully.
At a press conference in Cannes yesterday, veteran director Mike Nichols was challenged by an American journalist that he had "cut out an interracial love scene".
Nicols replied: "I did have it cut out after the first preview. I didn't think about the interracial element. I took part of the scene out of the movie because there was disappointment [in the preview audience] that these two were meant to be the good guys.
"They were meant to be more steadfast than this. I cut it down but not out. If you're looking for it, it's there."
John Travolta, who plays the Clinton figure, Jack Stanton, delighted questioners by revealing that President Bill Clinton, far from being hurt by the movie, invited Travolta to come to a party in character so that the two of them could do a speech together.
"I declined," Travolta said, "because I decided it was best to leave the character on the screen and not do parties. I think that shows the President's sense of humour. I was very tempted for a moment but I withheld my urge."
Emma Thompson interjected intriguingly at that point, saying: "He doesn't often hold his urge."
Thompson and Travolta both give excellent performances as the President and First Lady in the film which opens in Britain in August. Thompson plays Susan, a First Lady ruthlessly determined to help her husband to power and equally determined to survive in her marriage while implying her increasing suffering from the humiliations and embarrassments at the public disclosures of infidelities.
Thompson, in newly cropped, red hair set off by a bright orange sundress, stole the show at the press conference, clowning around when she wasn't speaking fluent French and translating for her colleagues.
She said she was "terrified" of the opening gala. "I hope the frock's all right," she said. "I was out in the sun yesterday so I've got all different colours."
Travolta said that Mr Clinton, who he knows socially, had not yet seen the film which has opened in America to good reviews but only average box office receipts.
It was interesting that Thompson and Travolta appeared to disagree about the cleverness of the characters they play in the film.
Thompson declared: "This woman has got more intelligence in her little finger than he's got in his whole body."
But Travolta claimed: "The man has high integrity in his political urges and I think he is a decent man. He is a complex human being.
"There's a naivete and innocence about this character which our own President has - I hope."
Thompson claimed she had not based her characterisation on Hillary Clinton: "I didn't want to do an imitation of her because that would be just an excuse to make people think `what has she got wrong?' It was more thrilling for me to create an imaginary character."
Anyway, she added, Ms Clinton spoke so rarely on television "partly because she is not given much of a voice. It's funny that the First Lady is the first person to hit the glass ceiling."
Travolta said he played the President as a composite of several presidents, "but mainly it reflects on Clinton".
Injecting an inevitable luvvyish touch, Thompson said that, in making the film, "we cried a lot actually.
"You get to a point where you think `that's so true about people!'"