Almost as soon as it was announced, the pact between Ted Cruz and John Kasich to team up and stop Donald Trump began unraveling. Kasich, you see, wasn't actually telling his supporters in Indiana and elsewhere to vote for Cruz.
Kasich, asked whom his supporters in Indiana should vote for: "I've never told them not to vote for me. They ought to vote for me."— Thomas Kaplan (@thomaskaplan) April 25, 2016
The commitment is simply that Kasich isn't expending campaign resources in Indiana, which is small potatoes because it's not like Kasich has a formidable Get Out the Vote operation or a massive ad budget anyway.
Here's how Kasich's chief strategist explains it.
We're not telling voters who to vote for in IN, only where we are going to spend resources to ultimately defeat Hillary. They get it.— John Weaver (@JWGOP) April 25, 2016
And it's just as well, because the basic idea of a Cruz-Kasich collaboration against Trump simply doesn't make sense. Trump has made some inflammatory comments on issues like immigration and the war against ISIS, but overall Trump occupies an ideological middle ground between Cruz on his right flank and Kasich on his left. Which means it's far from obvious that Cruz could convince his voters to vote tactically for Kasich over Trump.
Unless, that is, either of Trump's rivals were willing to offer the one argument against Trump that so far no GOP leader has been willing to make: Trump is such an unacceptable president that one should vote for anyone — including Hillary Clinton — to keep him out of the White House.
Nobody will make the only critique that matters
In a purely ideological context, there is no level of Cruz-Kasich collaboration that can stop Trump because Trump holds the central position ideologically.
But there is more to life than ideology.
One good reason a Ted Cruz supporter might have for tactically voting Kasich in order to block Trump from securing the nomination would be that Trump is manifestly unfit to serve as president — he's ignorant of policy, he flames racial resentment, and he's given multiple indications that he would wield power in a violent and lawless manner.
This is a perfectly good basis for ideologically motivated Republicans to back an ideologically hostile figure in pursuit of the greater good of stopping Trump.
The problem is that it's also a perfectly good reason for Republicans to back Hillary Clinton in November in pursuit of the greater good of stopping Trump.
And that's the bridge nobody in the leadership of the Republican Party has yet been willing to cross. On the contrary, both Kasich and Cruz tend to make the opposite argument — that one problem with Trump is that he's unelectable and likely to lose to Clinton in November.
It's completely understandable that people in GOP circles don't want to say they will betray the party's likely nominee in order to support a Democrat in the general election. But if you believe Trump is unfit for the presidency, that's the only reasonable course of action. And belief that Trump is unfit for the presidency is, at this moment, the only viable basis for an anti-Trump coalition.