“IF THE GOP does not nominate Donald Trump, the delegates need to be cleansed,” says an e-mail received a few days ago by Craig Dunn, a Republican delegate for Indiana’s fourth congressional district. It was one of many e-mails, calls and messages posted on the local Republican website to Mr Dunn from supporters of Donald Trump, the Republican front-runner, calling him a traitor and employing some colourful expletives. Mr Dunn had dared to say in an interview with Politico, a news organisation, that he would not support Mr Trump unless Satan were one vote away from the nomination. In that case, said Mr Dunn, he would “consider voting for Trump if he was the only alternative”.

The fight for Republican delegates has become fevered and rather nasty as Mr Trump scrambles to shore up support from 1,237 “bound” delegates, or 50% plus one vote, before the Republican convention in Cleveland, Ohio, in July. According to state party rules, a bound delegate assigned to Mr Trump in a primary election is obliged to vote for him in the convention’s first round of voting. Even Mr Dunn says that he would vote for Mr Trump if the property tycoon wins in his congressional district in Indiana’s primaries on May 3rd.

Mr Trump’s main rival, Ted Cruz, a Texan senator, no longer has a chance of reaching the magic number of 1,237 bound delegates, so he is focusing all his energy on stopping Mr Trump from reaching that threshold, in which case convention delegates continue to vote in at least two and possibly more rounds in a so-called contested convention. That notion riles Mr Trump. “The whole delegate system is a sham,” he told Fox News on April 26th. He has also called it “rigged” and “crooked” and accused his detractors of bribing delegates with trips and other perks. There is a certain amount of theatre in this. Anything that allows Mr Trump to claim outsider status is good for business; anything that makes his rivals look spooked or weak is doubly so. But his attacks bother party leaders, in particular in those states where Mr Trump lost and blamed his defeat on the delegate system.

“The process has been effective for decades,” says Pam Pollard, state party chairman of Oklahoma, where Mr Cruz won. “It’s a grass-root model driven by local party activists, not a sham,” says Mark Wynn, the Republican chairman in Indiana’s sixth congressional district. Many delegates are devoted volunteers and activists who have been loyal to the party for decades. Others say Mr Trump should have Googled the convention rules before he decided to run for president. They also point out that he has benefited from the system because his share of delegates thus far has exceeded his share of the vote.

The rules for the selection of convention delegates (2,472 for the Republicans and 4,765 for the Democrats) in a patchwork of more than 50 local elections, held in school gyms and other public buildings across the country, are not easy to follow. In many ways the primaries are hyper-democratic. In France, party apparatchiks choose their party’s presidential candidate without any input from voters. The same is true in Germany, where parties choose their candidate for the chancellorship. Yet in a contested convention, a few hundred delegates become kingmakers.

After the first round of voting—and even more so after the second and third rounds—most of them are free to vote for whomever they like, regardless of the wishes of primary voters. All eyes are now on Indiana, the only state to go to the polls on May 3rd and, apart from California, the most important of the states still to vote. The state is in the middle of two fierce fights on the Republican side. The first is a conventional one for votes. The second is for delegates whose loyalties can be relied on if they become unbound in Cleveland.

Mr Cruz criss-crossed Indiana on a bus in the second half of April. After stops in four different towns in Indiana on April 25th, he appeared at a rally on April 26th in a gym in Knightstown, a town of some 2,000 souls, where he attacked Mr Trump and Mrs Clinton in the same breath for their support of abortion choice, higher taxes and illegal immigrants (Mr Trump wants to send them back to wherever they came from, he said, and then let them in again). Mr Trump visited Indiana only once during the campaign, but on April 27th he flew to Indianapolis for a rally with Bob Knight, a popular basketball coach fond of throwing chairs in fits of temper.

Apart from trying to scoop up as many of the remaining candidates as possible, Mr Cruz wants to get delegates assigned to vote for Mr Trump on his side in a potential second ballot, especially in states he lost. Indiana’s delegate slate includes many party activists who are unlikely to vote for Mr Trump, unless they are required to, though some of them back Mr Kasich rather than Mr Cruz. “We will be an extended pit stop on the road to the second ballot,” predicts Pete Seat, a political consultant. Mr Seat thinks that Indiana delegates would support Mr Kasich on the second ballot because he is the most electable and the likeliest of the three to beat Mrs Clinton. (However, Mr Kasich can compete at the convention only if the Republican leadership changes its rule 40(b), which stipulates that to win the nomination a candidate must have won a majority of delegates in at least eight states.)

Jeff Cardwell, Indiana’s Republican state chairman, denies that whom they support was a criterion in the selection of delegates. He says delegates had to be Republicans “in good standing” and be deeply involved in party activities to make the cut. He points out that Rex Early, the chairman of Mr Trump’s campaign in Indiana, is one of the 57 delegates. Mr Cardwell rejoices in all the attention Indiana is getting this year. “Indiana could be a game changer,” he says, a role Hoosiers are unused to.

Until May 3rd many of Indiana’s delegates will be under lots of pressure from Trump supporters, who are inundating them with e-mails, phone calls and more. “The Trump camp started very late trying to win over delegates,” says John Hammond, one of Indiana’s two representatives on the Republican National Committee. What Mr Trump’s supporters lost in time they are now trying to make up with intensity. “We need a refresher course in civics,” sighs Mr Hammond. With only a couple of months left until the Republican convention, it may be a little late for that.