By Ted Cruz’s own admission, this is make or break.

As the Texas senator campaigns across Indiana ahead of Tuesday’s vital primary, he has warned his supporters he is fighting for the very future of his presidential hopes. If he allows Donald Trump, the Republican frontrunner, to win here, the battle for the coveted nomination is effectively over.

“I can’t emphasise enough how important the vote in Indiana is going to be and, frankly, it could be the deciding factor,” he wrote to supporters last week.

“Make no mistake, Indiana is absolutely pivotal. The bad news is that if Trump wins all the delegates in Indiana, his nomination could be all but determined.”

Mr Cruz is desperate to stop the New York tycoon from securing the 1,237 delegates he needs to secure the party’s nomination ahead of its convention in July.

It is mathematically impossible for Mr Cruz to himself win the nomination before the gathering in Cleveland; his only hope is of blocking Mr Trump and forcing a so-called contested convention, where he believes the party would unite around him. But if Mr Trump wins Indiana and its treasure trove of 57 delegates, it becomes increasingly likely he will become the party’s candidate.

Mr Cruz, a devout Christian, has been trying to reach out to Indiana’s social conservatives, of which there are a large number in the state. In recent days, he has been trying to incite controversy surrounding transgender people’s use of lavatories.

A number of states have passed laws that demand a person only use the toilet designated for the gender of their birth rather than how they identify. Campaigners for LGBT rights say the laws are discriminatory. But Mr Cruz has been telling voters he supports the measures and is seeking to contrast himself with Mr Trump.

“Donald Trump and Hillary Clinton both agree that grown men should be allowed to use the little girls’ restroom,” Mr Cruz said last week, at an event where he appeared with his daughters, aged seven and five.

In another attempt to reach out to conservatives, and to seek to highlight Mr Trump’s unpopularity among women voters, Mr Cruz named Carly Fiorina as his running mate, a step that is unprecedented at this stage in the campaign.

His campaign also did a deal with the third Republican candidate, John Kasich, whereby the Ohio Governor agreed not to campaign in Indiana in exchange for an undertaking from Mr Cruz to reciprocate the favour and stand aside in Oregon, which votes on 17 May, and New Mexico, which votes on 7 June. He has also boasted about winning the endorsement of Indiana Governor Mike Pence.

Yet it is unclear whether any of this will be enough to allow Mr Cruz to beat the thrice-married reality TV host he is facing off against.

Polls in Indiana have provided a mixed picture: one published last week suggested Mr Cruz had a clear lead over Mr Trump. But the majority suggest the advantage lies with the abrasive New Yorker. An average of polls collated by Real Clear Politics puts Mr Trump on 39 points, ahead of Mr Cruz on 35 and Mr Kasich on 17.

One poll published over the weekend by NBC News and the Wall Street Journal suggested Mr Trump had a lead of as many as 15 points over Mr Cruz, scoring the race 49, 34 and 13.

Meanwhile, among Democrats, polls suggest Hillary Clinton has a 50-44 advance over her rival, Bernie Sanders. Ms Clinton looks on course to secure the party’s nomination ahead of its convention, and her campaign is already looking towards the general election contest, most likely against Mr Trump.

Yesterday, Mr Cruz again said he could derail Mr Trump’s plans by winning Indiana.

“We are competing hard. I hope we do well here. I can tell you I’m barnstorming the state; we’re in a bus with my family, we’re doing everything we can to earn the votes of the men and women in this state,” he told ABC News.

“We’re going the distance. We’re competing the entire distance.”

The senator, who is trailing Mr Trump by 431 delegates, insisted he had a viable route to victory.