Today’s riddle: head-to-head match-ups

As of today, on Real Clear Politics, here are the outcomes of head-to-head match-up polling:

Trump v. Clinton:  Dems up by 3.4

Rubio v. Clinton:  GOP up by 5

Cruz v. Clinton:  GOP up by 1.5

Kasich v. Clinton: GOP up by 7.4

Trump v. Sanders:  Dems up by 8

Rubio v. Sanders:  Dems up by 3.3

Cruz v. Sanders:  Dems up by 9.7

Kasich v. Sanders:  Dems up by 0.5

Who wants to take a stab at explaining why, when Clinton is marketing herself as more electable than Sanders, the polling suggests that it’s the other way around?  And who are the people who would vote for the Republican in the match-up rather than switch their vote from Sanders to Clinton?