Sri Lanka, Jan. 28 -- Donald Trump on Saturday said he feels "sharper now than I did 20 years ago," reacting to recent attacks on his age and verbal gaffes by Republican presidential rival Nikki Haley.

Trump also said presidential candidates should have to take a cognitive test, apparently a response to a challenge from Haley, who has advocated the same policy, citing the age of Trump, 77, and Democratic President Joe Biden, 81.

Trump was speaking at a rally in Nevada, ahead of the next vote in the Republican presidential nominating race, a caucus in the state on Feb. 8. In recent days Haley has accused former Republican President Trump of being confused and has questioned his ability to be president at his age.

Trump has recently made...