There are three candidates representing your father’s Republican Party. They are Jeb Bush, John Kasich and Chris Christy. All three are near the bottom in polling.
Reagan and Bush One were in that party. The cobbled together an aggressive military posture, lower taxes and traditionalism into a single ideology. The concept was called fusion. They steered clear of taking any of them very far if at all lest they lose the other two.
Along came Bush II who thought his job was to actually do these things. We invaded two countries, cut taxes and embedded religion into the structure of government.
He made each of the factions feel entitled to take over the party. Traditionalism became the religious right. A strong military became anti immigration and lower taxes became libertarianism. Each started doing its own fundraising, its own think tanks and its own publications. None of them has much interest in a winning Republican Presidency unless it is theirs.
Lots of people from each of the factions recognize their own faction will probably not be successful. Their view is they do not want the establishment party of Bush I back in either so they don’t support the three musketeers representing it.
They see voting for a candidate from their own faction as throwing away a vote because he/she will not win. They refuse to vote for a Democrat and old GOP party guy. Along comes another candidate who puts his figure in the eyes of everyone they dislike.
His name is Trump.
[An article about this kind of politics is linked in comments.]