The mental ability and age of the United States' presidential candidates took center stage on the campaign trail on Saturday, following a report that suggested President Joe Biden was suffering memory lapses. Former President Donald Trump accused both Biden, the Democrat he will likely face in November's general election, and Nikki Haley, Trump's last remaining rival for the Republican presidential nomination, of lacking the mental capacity to be president. Haley - like Trump, campaigning in South Carolina where the two will meet in a primary election on Feb. 24 - went after both men, calling Trump mentally deficient and saying Biden is too old to be president.