One of the most watched subplots of this year’s Republican National Convention is the feud between Donald Trump and Ohio Governor John Kasich. And that’s odd. Trump was relatively nice to Kasich. His nickname was “1-for-38 Kasich.” The governor can’t even argue the math of that one.

And Trump is reported to have tried very hard to get Kasich on the ticket.

Donald Trump and John Kasich’s teams are at war over whether the Republican presidential nominee ever seriously wanted the Ohio governor to join the ticket.

Multiple sources close to Kasich said Trump’s son, Donald Jr., tried to entice Kasich with a position as the most powerful vice president in history, but he turned it down. Kasich would have been in charge of all domestic and foreign policy in a Trump White House, Kasich sources said. . .

Kasich sources said the vice presidential back-and-forth began when Donald Trump Jr. reached out to Weaver, Kasich’s adviser, shortly after Kasich dropped out of the race in May. . .

Another Kasich source says there were also separate instances of Trump allies reaching out to Kasich allies asking whether the Ohio governor might consider the VP slot.

Manafort also described the vice presidency in a Trump administration as being similar to the COO of a company in an interview with the Huffington Post in May, a role that would appear consistent with the job being described by Kasich sources.

“He needs an experienced person to do the part of the job he doesn’t want to do. He seems himself more as the chairman of the board, than even the CEO, let alone the COO,” Manafort said. . .

Trump sources have acknowledged. . .that long before Trump settled on Indiana Gov. Mike Pence for his running mate, top Trump aides viewed Kasich as their best bet for winning the White House in November.

That’s how much Trump reportedly wanted Kasich. So why has Kasich refused to participate? Typically, a governor will welcome convention-goers, even if they’re from the other party. Not this time.

The Republican National Committee and the Trump campaign launched a concerted and sometimes public effort to woo Kasich back into the fold ahead in the weeks before the convention. But Kasich rebuked their advances.

This week relations between the two camps have grown even more strained after Manafort told MSNBC that Kasich was “embarrassing his state” by skipping the convention.

While Trump got personal in his attacks against “Lyin’ Ted” Cruz, “Little Marco” Rubio. “Low Energy” Bush, “Horseface” Fiorina, and “Truly Weird” Rand Paul, Trump always treated Kasich gently. Part of it was that Kasich had no chance. Another is that in poll after poll, Kasich was the Republican who always beat Hillary Clinton “if the election were held today.” That probably also led to the vice president overture.

The thing is, this is not personality. It’s policy, and Kasich is steadfast, according to the Washington Examiner.

“The governor has said that the nominee has to have a positive, inclusive vision, and unless there is a Saul-on-the-road-to-Damascus conversion, he is not going to support [Trump],” Kasich spokesman Chris Schrimpf told me in a phone conversation Tuesday. “Whatever happens in Ohio for Donald Trump is a choice that Donald Trump will make, based on how he chooses to campaign.”

It appears that Kasich may have the last laugh. No Republican has ever won the White House without Ohio, and that means organization, but Kasich isn’t interested in helping.

Walk around the Republican convention and talk to Ohioans, to Republicans from around the country, and to party strategists about the feud between Donald Trump and John Kasich, and here’s the short version of what you’ll hear: Kasich is being a jerk, but Trump is crazy to fight with him.

The Trump-Kasich spat is more than a sideshow. It’s at the very heart of the presidential campaign. Of the various ways, none of them easy, for Trump to win the White House, the most direct is: Win all the states Mitt Romney won in 2012, and then, on top of that, win Ohio, Pennsylvania and Florida. Any other path starts to get really complicated. So a Republican who loses Ohio loses the presidency.

We reported elsewhere that Ted Cruz has his sights on 2020, and that could be what Kasich is thinking, too.

Trump campaign chief Paul Manafort said of Kasich during at a breakfast meeting, reported by the New York Times. “Negotiations broke down because [Kasich campaign “guru”] John Weaver thinks that John Kasich will have a better chance to be president by not supporting Donald Trump.” . . .

Weaver [has] called the Trump campaign a “clown show,” run by “knuckleheads.”

Trump himself shot back. Calling in to Fox News on Monday night, Trump said of Kasich, “I beat him very, very soundly. And you have to understand, this was a contentious, some people say the most contentious primary they have ever seen in either party. If I were him and gotten beaten that badly I probably wouldn’t show up either.” . . .

Kasich is famous for having a difficult personality. But as far as Trump is concerned, Kasich is the governor of a swing state Trump cannot afford to lose. Kasich controls political resources in that critical swing state. So it really doesn’t matter that many see Kasich as a sore loser after the GOP primaries. Winners have to manage losers wisely. Or, at a minimum, not attack them publicly.

The entire campaign this year may come down to what John Kasich does. Or does not do.