The two most powerful forces at the Republican convention
They are (1) Cruz supporters; and (2) the RNC establishment.
The Cruz supporters are the most dangerous to Trump. They will use any dirty trick available to get their guy nominated.
The RNC establishment (let’s call them the RNCe) is a distinct subset of the GOPe. The never-Trumpers within the GOPe are not from the RNCe. The RNCe is protective of the Republican organization, to which they owe their positions. Unlike certain never-Trumpers, the very last thing the RNCe wants is for there to be any sort of third party candidacy, whether from Cruz, Trump, or anyone else.
The RNCe has no love for Trump, but they also have no love for Cruz and they genuinely value the perception that the convention process is fair. Thus they will certainly not support any dirty tricks that would result in the perception that Cruz stole the nomination from Trump (because that would result in a weaker Republican Party and a nominee they still don’t like and who can’t beat Hillary unless she dies from a stroke before the election and even then Cruz still might lose).
If Trump simply comes to the convention with fewer than 1,237 delegates, they would prefer that either Trump wins or nobody wins rather than Cruz wins the first ballot. After the first ballot they would prefer that someone more moderate comes in to take the nomination. Someone like Susana Martinez, or any of the other not-Cruz possibilities I mentioned in that blog post.