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Ohio Governor and GOP presidential hopeful John Kasich spoke to a crowd of about 300 supporters Thursday afternoon at Castaway Portland, April 28, 2016.

(Beth Nakamura/Staff)

By Jonathan Bernstein

It is simply astonishing how destructive Ohio Gov. John Kasich's campaign has been to the Republican Party.

Right now, the evidence is on full view in Indiana. As part of a deal with Texas Sen. Ted Cruz's campaign, Kasich isn't campaigning in the Hoosier State, which votes on Tuesday. But he and his supporters are still telling people to vote for him -- even though a vote for the Ohio governor is basically a vote for Donald Trump. If Kasich's supporters in Indiana want him to have any chance at the nomination, they will vote for Cruz.

Here's why.

Trump has a slim lead in current polling averages in Indiana. He's at 37 percent, with Cruz close behind at 35 percent. Kasich is far behind with 16 percent. If Kasich's voters switch to Cruz (and all else remains equal), then Cruz will win big. If they stay put, Trump might narrowly prevail. Indiana has 57 delegates: 30 will go to the statewide winner; of the remaining 27, 3 each will go to whomever wins in the state's nine congressional districts.

Indiana Gov. Mike Pence has given Cruz a lukewarm endorsement, so perhaps the Texas senator will get a boost from that. But there are signs Trump is rallying nationwide, so he may be doing better than the Indiana polls indicate.

For Kasich to have a shot at the nomination, he has to prevent Trump from getting to 1,237 delegates on the first ballot at the Republican convention. It doesn't matter how many delegates Cruz has at that point, since he can't get to 1,237. (Cruz can't get close to delegates on the first ballot, even if he wins all of the unbound, uncommitted delegates. But if Cruz clearly has the delegates to win on the second ballot, it's possible that he might be able to win on the first ballot after all if Kasich and Marco Rubio release the delegates they can release and Cruz gets all of them.)

All that matters for Cruz and Kasich is reaching a second ballot, when now-bound delegates are free to vote their preferences. After that, if Cruz can't put together a majority, it will become possible for someone else to win. I don't think Kasich stands much of a chance even in that unlikely chain of events, but at least it's possible.

Trump's big sweep in New York on April 19 and in the five states that voted this week have put the reality-TV star ahead of the pace he needs to reach 1,237 bound and committed delegates by the end of the primaries and caucuses on June 7. But he still needs to win plenty of delegates in Indiana and California to reach that mark. (Trump can still make the delegate count of even if he's shut out in Indiana, but it would raise the target of how many he needs to win in California. If Trump sweeps in Indiana, he'll need to win only a relatively small number of congressional districts in California to reach 1,237.)

And it isn't just about numbers. If Trump can win big in Indiana, expect any Republican party actors who would ever consider supporting him to go ahead and accept him as the nominee. And that support, in turn, will help Trump do well in California on June 7.

Kasich is also helping Trump by refusing to debate Cruz one on one after Trump dropped out of the debates. The Ohio governor has thus denied himself as well as Cruz free media exposure and a chance to make Trump look cowardly and arrogant for opting out.

A normal candidate in Kasich's position would have dropped out long before now. By failing to do so, he helped end the chances of the mainstream conservatives who were running. It's impossible to say what would have happened if Kasich has dropped out after New Hampshire, for example, or after South Carolina and Nevada -- but the odds are strong that the GOP nomination fight would have turned out differently.

Is it just an ego trip? Does he unfathomably misunderstand the rules of the game? Have party actors foolishly advised him to do what he's been doing? Perhaps we'll find out after the campaign ends.

But for now, it's pretty simple: Kasich is Donald Trump's best weapon, and he has been since February.

Jonathan Bernstein is a Bloomberg View columnist covering U.S. politics.

For more columns from Bloomberg View, visit http://www.bloomberg.com/view.

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