“In a world where US politics is still dominated by the two current major political parties, Democratic and Republican, the first female POTUS will be a Republican.”

When conservatives like someone, they unreservedly support them. This especially applies when conservative men, who still make up most of Republican leadership, particularly admire a specific girl or woman. A casual large-scale example is the fanbases of many female characters from media popular among conservatives. Compare this to the fanbase discourse of any character from media popular among non-conservatives.

Though a conservative man's protégés may usually be young men, when he chooses to mentor a young woman, she often becomes the favorite. There exists a belief she is extra special because he noticed her as worthy of being mentored. While he opens metaphorical doors for all his protégés, he goes the extra mile to literally and figuratively open them for the brilliant singular girl who consistently exceeds his expectations.

Because Republicans place party cohesion above individual idealism, once the leadership has a special girl selected, the basic voters will fall in line. Not only will they fall in line—they too will genuinely believe this woman is "different" from, and therefore better than, other women. The voters will over idealize her, lose their minds a little for her, and vote their new icon into highest office.

Of course, once she's at the political pinnacle, they will likely turn on her and hate her with concentrated venom when she fails to live up to this impossible ideal.

Current Democrats and non-Republican voters do not put party cohesion above individual idealism. Furthermore, their ideals are too diverse and clash, which is why they would never be able to pick a single person to over romanticize into office. Many do not admit to their own inherent sexism, and therefore no woman in the foreseeable future will be enthusiastically backed by the majority of the Democratic voters, much less sufficiently backed by those of the swing states.