No, the bartender does not have salt water, nor can you drink salt water.
Of course he has salt water. Just because you, along with that crowd in the pub, ignore the salt water because you're collectively obsessed with debating a self-restricted choice between beer and soda doesn't mean that the salt water isn't there. Ignoring a choice does not mean it doesn't exist.
For the presidential election expecting people that poll at less than 5% to win is a similar choice. The best chance anyone not named Clinton or Trump has of being elected this year is Johnson, and currently he has less than a 1% chance. Realistically, the only 2 people with a shot are Clinton arena Trump.
A self-fulfilling prophecy then? It's not "realistic" because you choose to make it not "realistic". Those polls are not logical or physical restrictions being placed on the outcome, they are just the choices made by individuals, all of whom have a whole range of choices available other than Clinton or Trump. There is nothing stopping any individual from making another choice, nor them collectively doing so.
Seems akin to the strategy used by anti-immigrant groups. First they claim it is not "realistic" to accept refugees because it would lead to all sorts of problems, then they go create all sorts of problems whenever refugees get accepted, and then say "see that it was not realistic?"
The only people making a result other than Trump or Clinton not "realistic" are the ones choosing either Trump or Clinton, ironically enough for a good part based on their own claims of another choice not being "realistic".
Please explain what choices we as a country could make which result in no one being President.
If you're not even willing to accept that you, as a country, have choices which would result in another president than Trump or Clinton, then why should I expect you to accept that you, as a country, have choices resulting in no one being president?
But since you asked anyway, abolishing the position of president would seem to do it.