In the week leading up to Indiana's Republican presidential primary, candidate Ted Cruz repeated over and over how "critically important" the state is to stopping front-runner Donald Trump from getting the GOP nomination. (Sarah Parnass/The Washington Post)

Inside Ted Cruz’s second-floor campaign office here on a recent afternoon, there were telltale signs of an operation in overdrive: dozens of volunteers calling voters and re­fueling with Mountain Dew, coffee and snacks; staffers busily working on laptops; and an ambitious message on a whiteboard: “Our Goal Today = 20,000 Calls.”

But there were also indications of trouble. Volunteers said they were hearing misgivings from voters — many rooted in insults that front-runner Donald Trump had hurled at Cruz.

Most people who express reservations, explained Megan Kerr, 17, of Fishers, Ind., “are concerned with the nickname he’s been given — ‘Lyin’ Ted.’ ” Frank Cerrone, 68, of Perry Township, Ind., also said “there is some idea that Ted Cruz is rigging the system,” another Trump attack.

Cruz came to Indiana to try to resuscitate his flagging campaign at a pivotal moment in the Republican presidential race. But with just one day of campaigning left until Tuesday’s vote — and after a series of desperation measures — the freshman senator from Texas is on the verge of a defeat that would ravage his campaign and raise new questions about whether his mission to stop the mogul has become futile.

Ted Cruz recreated a scene from the movie "Hoosiers" at his April 26 rally in Knightstown, Ind. Here's how his reenactment compares to the original movie scene. (Peter Stevenson/The Washington Post)

An NBC News-Wall Street Journal-Marist poll released Sunday showed Trump leading Cruz by 15 points in Indiana. Other recent public polls have shown Trump leading by narrower margins.

Supporters hoped that Indiana, which has similarities to other Midwestern states Cruz has won, would be able to heal the deep wounds left by Cruz’s blowout losses in six straight states. But it has been very difficult for Cruz to gain traction in the face of relentless attacks from Trump and hiccups in his own effort.

Nevertheless, Cruz is waging an aggressive final push in the state, including three stops on Sunday. He also appeared on all five Sunday-morning news shows.

“It is an incredibly important state. We are competing hard. I hope we do well here,” Cruz said on ABC’s “This Week With George Stephanopoulos.” “I can tell you I’m barnstorming the state. We’re in a bus with my family. We’re doing everything we can.”

A Trump win in Indiana would not only move the mogul closer to the 1,237 delegates he needs to clinch the nomination, it also would leave Cruz without a primary win in four weeks heading into the final stage of the campaign.

Trump plans to contest the Hoosier State vigorously in the final hours of the contest, scheduling two rallies for Monday. He has zeroed in on Indiana’s manufacturing job losses at rallies and has accused Cruz of being dishonest and trying to wrest the nomination away from him unfairly by seeking to install loyal delegates to the Republican National Convention even in states where Trump won.

“Right now after this show, I’m going to Indiana. We’re going to have Bobby Knight. We’re going to have other people that are unbelievable,” Trump said on “Fox News Sunday,” mentioning the popular former Indiana University men’s basketball who is campaigning for him.

Cruz’s Indiana strategy is both urgent and unconventional. On the campaign trail, he has en­couraged Republicans to reject Trump’s brash style in favor of a steadier and more positive approach — a jarring argument for someone who has built his political career on fighting with Republican leaders and creating turbulence in his party.

“It is the common sense and good judgment of the Hoosier State that is the one thing that stands between us and plunging over the cliff,” Cruz said at a convention-hall rally in South Bend, Ind., on Thursday.

He continued: “The people of Indiana will make a choice: Do we want to get behind a campaign that is based on yelling and screaming and cursing and insults? Or do we want to unify behind a positive, optimistic, ­forward-looking conservative campaign?”

At Cruz’s campaign office here in Indianapolis last Tuesday, animosity toward Trump was on clear display. “Hillary beats Trump very bad — double digits,” said one volunteer making the case for Cruz over the phone.

Cerrone said that when he talks to Trump backers, they are generally impolite.

“Most of the Donald Trump supporters are really rude,” he said. “And that’s not surprising, because so is Donald Trump.”

Cruz named former Hewlett-Packard chief executive Carly Fiorina as his vice-presidential running mate last week, the kind of decision not typically made so early in a campaign. Fiorina clashed with Trump during her own campaign for president and has been helping Cruz cast him as a bully in Indiana.

The two have also sought to tie Trump to Democratic front-runner Hillary Clinton. Cruz released a pair of TV commercials over the weekend arguing that Trump and Clinton are “two sides of the same coin” on taxes, transgender rights, health care and other issues.

Cruz is hoping his deal with Ohio Gov. John Kasich to effectively take on Trump one-on-one in Indiana will swing voters toward him. But both sides have muddled the arrangement, and the NBC poll out Sunday showed that 58 percent of GOP voters disliked the bargain. (Kasich is also pulling 13 percent of the vote.)

Even a surprise Friday endorsement from Gov. Mike Pence (R) was not without a snag. The governor prefaced his Cruz endorsement with praise for Trump and an assertion that he was not against any candidate.

“I think he gave me more of an endorsement than he gave Cruz,” Trump said on “Fox News Sunday.”

Cruz is trying to make the most of Pence’s stamp of approval. He released a radio ad over the weekend with a clip of the governor praising him for taking on his party’s leaders in Washington.

Undecided voters such as Frank Swiss of Carmel, Ind., illustrate part of Cruz’s challenge. Swiss, who said he was “interested” in Kasich and opposes Trump, spoke to Cruz at an Indianapolis restaurant last Wednesday. He said he found the senator “charismatic” and “down to earth.” But not enough to commit to voting for him.

“It’s hard,” Swiss said. “This is a tough one.”