Republican presidential candidate Ted Cruz greets supporters at a campaign event at Shapiro's Delicatessen in Indianapolis on Thursday. (Aaron P. Bernstein/Reuters)

Republican groups, leaders and candidates opposed to Donald Trump increasingly see the Indiana primary as a central front in their last-ditch efforts to stop him from clinching the GOP presidential nomination.

But fractures in the movement, and a clear lack of urgency among local Republicans to unite against Trump, are undercutting their ability to deliver the state.

With Trump poised to rack up more delegates in five Eastern states on Tuesday, Indiana’s May 3 primary is shaping up as a must-win for Sen. Ted Cruz (Tex.), who is attempting to win enough delegates to force a contested Republican convention in ­Cleveland. It also is one of the last, best chances for outside ­forces helping Cruz and Ohio Gov. John Kasich to slow the GOP front-runner.

“Come the evening of May 3 or at the least the morning of May 4, I think we will know whether Donald Trump will be the presumptive nominee,” said Pete Seat, an Indiana Republican strategist and consultant to Kasich’s long-shotcampaign.

As they have been in other states, the anti-Trump groups here are riven by divisions over strategy and tactics, and are limited in their financial resources. Indiana marks at least the fifth contest that opponents have declared as the moment to stop Trump, from the Iowa caucuses in February to the Wisconsin primary early this month.

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“You go into war with the army that you have,” said Rory Cooper, a senior adviser to Never­Means­Never PAC, which has endorsed Cruz in Indiana and plans to run digital ads here — even as it backs Kasich in some other states. “Kasich and Cruz need to focus on their presidential campaigns. We have slightly different interests.”

The Club for Growth, an anti-Trump group that supports Cruz, plans to make an investment in Indiana comparable to the $2 million it spent in Wisconsin, said David M. McIntosh, the former Indiana congressman who runs the organization. The group’s first Indiana TV ad, which began airing Friday, focuses its attack on Kasich, arguing that a vote for the Ohio governor “actually helps Trump, by dividing the opposition.”

Pointing to Trump’s blowout win in New York this past week, the Kasich campaign released a memo arguing that “Never Trump” forces­ “missed opportunities” to take on Trump “by not engaging in any serious ways.”

Cruz and his backers are hopeful that in Indiana, he can repeat the kind of victories he enjoyed in Iowa and Wisconsin, although there has been no reliable polling in the state. He campaigned at an Indianapolis deli Thursday afternoon and spoke at the state Republican Party’s spring dinner Thursday night.

“Indiana is going to be a battleground,” Cruz said as he made his way through Shapiro’s Delicatessen downtown, where the owner hinted that he was a Kasich supporter. Later at the dinner, he promised to barnstorm the state and made an even more urgent plea: “The entire country — her eyes on are on this state.”

Recently, Cruz’s father, Rafael Cruz, spent the better part of two weeks campaigning in the state. The pastor spoke to groups as small as 20 people, hoping to re-create the ripple effect with religious voters who boosted Cruz’s campaign in Iowa and Wisconsin.

However, some of the factors that turned Wisconsin into a Cruz rout are missing in Indiana. Wisconsin’s GOP leaders, led by Gov. Scott Walker, a former 2016 presidential candidate, quickly coalesced behind Cruz. By the time Cruz and Trump started campaigning in the state, influential Wisconsin radio talkers had been pummeling Trump for months, making his brand toxic.

Protesters carrying American and Mexican flags shut down a highway leading to the site of a rally by Republican presidential candidate Donald Trump in Arizona. (Reuters)

That isn’t the case in Indiana, where radio hosts such as Indianapolis’s Tony Katz and Fort Wayne’s Charly Butcher are more even­handed when they talk about the primary.

“To think that there is a massive or overwhelming anti-Trump sentiment in Indiana would be false,” Katz said.

Rallying supporters at the state fairgrounds here this past week, Trump singled out Carrier, a manufacturer of air conditioners, for deciding to move jobs from Indiana to Mexico. He won cheers when he vowed, as he has many times before, that he would not allow such decisions to happen as president without hitting the company with a tax penalty.

Trump closed by raising the stakes of Indiana’s primary.

“You’re going to go out and vote, and you’re going look back at that vote — and you’re going to say that was the single greatest and most important vote that you’ve ever cast,” Trump said to applause.

Indiana’s elected Republicans have been straddling the fence. Gov. Mike Pence, who has not ruled out making an endorsement, met with Trump before his Wednesday rally and met with Cruz on Thursday. Sen. Daniel Coats and four congressmen endorsed candidates who have since quit the race; none have made a new endorsement.

“I’m an elected delegate now, and I take that job seriously,” said Rep. Todd Rokita, who backed Sen. Marco Rubio (Fla.) and is now neutral. “I haven’t endorsed anyone because I don’t know anyone as well as I know Marco. So I’m going to be getting information from everyone before we get to Cleveland.”

Their reticence has frustrated Trump’s foes.

“My prediction is that the elected leaders will be wimpy in Indiana,” McIntosh said.

Four years ago, Indiana’s tea party drew the blueprint for a unified conservative primary campaign. Hoosiers for a Conservative Senate, an ad hoc group of activists, met in person to endorse one candidate — then-State Treasurer Richard Mourdock — to challenge incumbent Sen. Richard G. Lugar (R). Mourdock won in a landslide, helped by the fact that no one else was splitting the vote.

There is no similar teamwork in 2016.

“I met Ted Cruz personally; a lot of us activists have,” said Greg Fettig, a state legislative candidate and leader of Hoosiers for a Conservative Senate. “That being said, a lot of the activists are Trump all the way. I’d be okay with either one, Trump or Cruz. And let’s just say that my wife and I didn’t vote for the same candidate.”

Further muddling the picture is Kasich. His allies see similarities between him and Mitch Daniels, the popular former Indiana governor, that could boost him in parts of the state. And his campaign has expressed confidence that Indiana’s delegates would look upon his candidacy favorably if the convention goes to a second ballot.

It has been 40 years since a Republican presidential primary lasted long enough to run through Indiana. In 1976, the state went for Ronald Reagan over President Gerald R. Ford by 16,266 votes out of more than 630,000 cast.

Today, about 40 percent of the primary votes come from greater Indianapolis, where Trump and Cruz kicked off their efforts.

Trump’s campaign is setting high expectations.

“Trump’s going to win Indiana by big numbers,” said Rex Early, a former Indiana GOP chairman who is leading Trump’s statewide campaign. “At the very least, he will take eight out of the nine districts.”

Weigel reported from Washington.