The conservative wing of the GOP was determined to get Boehner out--and they want to get McConnell out of the Senate too. They want the GOP to coalesce around a conservative candidate and shut the "mainstream Republicans" (Republicans they consider too moderate) out of the picture.
They don't see coalescing around a moderate an option. In their minds, the moderates must capitulate to the conservatives.
Ted Cruz expressed their big worry today at the "Value Voters Summit":
“Washington wants us divided. Washington wants conservatives splintered,”Cruz said Friday. “They want a chunk of evangelicals over here, a chunk of conservatives over here, a chunk of libertarians over here, a chunk of tea party folks over here. That’s how, if we are splintered, that a moderate establishment candidate runs up the middle with 23 percent of the vote, steals the nomination, and then loses to Hillary Clinton in the general election.”
As long as we Democrats nominate Clinton, we win. if we nominate Bernie, they can beat us.