It’s just amazing how bad the Republican tickets in 2008 and 2012 were. You gotta think the Democrats somehow had a hand in that.
It was called not having a choice. The same people selected both the republican and democrat candidates, so no matter who won, their agenda would get through.
In 2016, the republicans knew Jeb! was a stone cold loser, but they thought he could pull about 20% of the vote in the primaries, but knew that even republicans were sick of the Bushes. The plan was Jeb vs Hillary. They did two things they thought would steer the nomination to Jeb. First, they allowed an unprecedented number of candidates, figuring they'd split and keeping any single candidate from being the anti-Jeb candidate. Then they made Florida winner take all. They figured Jeb, like most candidates, would carry at least a plurality in his home state. So, the plan was to let him rack up a few delegates, split the anti-Jeb vote among the others, and then when they hit Florida, BOOM, Jeb, with 23 or 24% of the votes would get a bunch of delegates, and they could start the "Jeb is inevitable" mantra.
Turns out people hated the Bushes even more than the political class thought they did, and the political class knew the Bushes were so hated that Jeb! didn't even use his last name in campaign materials.