“Official food taster” is one heck of a job. It’s putting your life on the line, one bite of food at a time. If someone wants to poison the king, they’ll have to go through you first. Only afforded to the extremely powerful, they apparently were the norm back in medieval times (or so the movies have told us), but do they still exist? And if so, does the president have one?
“No, he doesn't.
When the President stops in at a local restaurant during his travels in the US, Secret Service will depend on the fact that his exact stop is unknown to all but a very limited few and the fact that restaurants do not, as a rule, have poisoned food on hand. They might, however, watch as a burger or salad is being made.
Obviously, there’s a lot more that goes into making sure that everything the president and his family eats is safe, but this should give you an idea of how it goes down. Also, keep in mind that most poisons are relatively slow-acting, so having someone take a bite a minute or two before the president does wouldn’t actually accomplish much.