Donald Trump on Saturday night suggested President Joe Biden “should have to take a cognitive test,” only to confuse who administered the test to him in the next sentence. The former president and presumptive Republican nominee referred to Texas Republican Ronny Jackson, who was the White House physician for part of his presidency, as “Ronny Johnson.” The moment came as Trump was questioning Biden’s mental acuity, something he often does on the campaign trail and social media. “He doesn’t even know what the word ‘inflation’ means. I think he should take a cognitive test like I did,” the former…