Washington - With each scripted speech, shift in policy and attempt to whitewash his past behaviour, Donald Trump is brazenly betting that voters now settling on their choice for president are willing to shove aside all that came before his late-in-the-campaign recalibration.It's a deeply uncertain proposition given Trump's staggeringly negative standing with most Americans.Polls show more than half believe the Republican nominee is unqualified to be president and is biased against women and minorities.But his strategy doesn't require moving huge segments of the electorate.Child careSeven weeks from the November 8 election and with absentee ballots already available in a few states, Trump and Democrat Hillary Clinton are fighting for a small sliver of undecided voters who, in many cases, simply can't stomach either."What these candidates are trying to convince the voters of is, 'I'm not as bad as the other one,'" said Neil Newhouse, a Republican pollster.In recent weeks, Trump's attempts to make that case have sometimes left him looking like a candidate with little resemblance to the one who stunned the Republican Party during the primaries.He now largely reads speeches off teleprompters despite casting aspersions on other politicians for relying on the devices. He's rolled out proposals on policies in which he's shown no previous interest, including child care and paid family leave. And he's made overtures to minorities, including blacks and Hispanics, groups with whom he has minimal support.Trump's latest attempt to persuade voters that he's the lesser of two evils came on Friday, when he abruptly reversed course on his lie that President Barack Obama was not born in the United States.Trump's role as chief promoter of the conspiracy theory about the nation's first black president has left him with almost no support among African-Americans and has turned off moderates who bristle at its racist undertones.Trump's newfound acceptance of Obama's birthplace seems unlikely to sway many of those voters. He offered no apology for pushing the falsehood for years and instead said the rumours originated with Clinton, another inaccurate claim.Negative ads"Despite what his campaign strategists told him to say today, I think he still believes that the president wasn't born in America," said Dan Pfeiffer, a former Obama adviser who was tasked with releasing the president's long-form birth certificate to reporters in 2011.Clinton advisers say their data show no fundamental shift in the public's perception of Trump, despite preference polls that are tightening nationally and in some battleground states. They believe a summer spent blasting the airwaves with television ads highlighting Trump's bellicose behaviour and questionable business practices, as well as a series of sharply critical speeches from Clinton, have largely cemented voters' negative view of the real estate mogul and made it impossible for his pivot to take hold."Trump has been defined," said Celinda Lake, a Democratic pollster. She said that's particularly true among women, who "think he's the worst date they've ever been on."A recent Quinnipiac poll showed 59% of likely voters believe the way Trump talks "appeals to bigotry." Among likely women voters, 62% held that view.Clinton's strategy has echoes of the approach Obama used to define Mitt Romney in 2012. Obama's campaign spent the summer pummelling the Republican challenger with negative ads painting him as a cold-hearted businessman with little regard for middle-class Americans.Romney was hamstrung by his inability to access general election money until after the GOP convention in late August and had few ways to defend himself and never recovered.Political impulsesObama also had a distinct advantage over Clinton: His own favourability rating was solid, making him an appealing alternative for voters turned off by Democrats' portrayal of Romney.Clinton doesn't have that same reservoir of goodwill and her standing with voters is as shaky as Trump's, though her chief weakness is trustworthiness.Trump aides have long believed voters' doubts about Clinton created an opening for the Republican, if he could control his worst political impulses. He showed no ability to do that throughout the summer, but was finally persuaded by a new team of advisers who presented him with plummeting polls and a stark warning that he was on the path to defeat.Aides say the tightening polls have validated the new approach in Trump's eyes. He also has benefited from a rough patch for Clinton, including her campaign's secretive handling of her recent pneumonia diagnosis and a steady drip of revelations about her use of a private email system at the State Department.