(travel) Charles is a sales representative. He a lot.
Have to is not a modal verb. It changes like an ordinary verb. For example, like "want to do something".
Mike has to leave.
Mike doesn't have to leave.
Does Mike have to leave?
have to = to be obliged to do that, it is necessary to do thatdo not have to = it is not necessary to do that, there is no need to do that