This is kind of a no-win situation in terms of optics. If he walks around and falls, the uncharitable scream "Clearly incompetent!". If he, say, sat in a wheelchair to reduce the falling over percentage to literal 0, they'd scream "Clearly incompetent!". If he'd use some assisting device like a cane, they'd also scream "Clearly incompetent!". And if he was as young as Obama, they'd criticize his tan suit.
There will always be something. Because the entire battle around optics is designed to distract from the much more important issue of policy and strategic ability, so by design there must always be something no matter how petty.