We often hear liberals tell us we should vote for one candidate over another candidate because they'll be our first president of this race or that gender. For example, we hear liberals tell us we should vote for Obama over another candidate because he'll be our first black president. Likewise, the reason we should vote for Hillary over another candidate is because she'll be our first female president.
At the same time, it's interesting to note that, for the generation born under Obama's term (i.e. those who are now about 7 years old or less), they'll only have known a black president. If we then assume Hillary will become the next president, then for the generation that's only known Obama and/or Hillary as president, they'll only have known a black and/or female president. If this trend continues until they're eligible to vote, then they'll have known a black and/or female president.
Now, let us take this same principle, and ask, why couldn't these upcoming generations, when they come of age to vote, argue along these lines and say they should vote for a white male for president since they'll never have known a white male president? Suppose the choice is between a white male for president vs. a white female for president, and suppose they've only known a string of white female presidents, then for them gender could be the deciding factor.
Sure, it won't be the first white male president in the whole of American history. (Though, in our hypothetical, it won't be the first female president either.) But it will be the first white male president in their history. So the same principle would still seem to be applicable, i.e., preferencing one person over another person because that person will be our first [blank] president.