And the delegates can make it completely impossible by agreeing to keep rule 40.
So what will happen at the convention is, Priebus will step up to the mike and announce "The proposal put forth is to keep rule 40! All those in favor?"
[THUNDEROUS SHOUTS OF "AYE!"]
"All those opposed?"
[crickets]
Priebus slams the gavel. "The 'Nays' have it! The proposal to keep Rule 40 is turned down; Rule 40 is removed!"
A lot of the delegates are appointed by the GOP. They may be assigned to one of the candidates for the first ballot but their allegiance is to the GOP.