By Tim Reid WASHINGTON (Reuters) -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 …