‘If we win Indiana, it’s over’: Trump talks tough ahead of Indiana primary

WASHINGTON – Donald Trump could become unstoppable on his path toward the Republican presidential nomination if he wins today’s Indiana primary.

Victory would give him a valuable haul of delegates.

That would vastly increase the likelihood that he will crack the magic number of 1,237 on the final day of primary voting on June 7, allowing a first-ballot victory at the summer convention.

“Honestly, if we win Indiana, it’s over. It’s over,” Trump told a rally on Monday.

The billionaire said of his rivals: “They’re finished. They’re gone (if we win).”

His rivals wouldn’t necessarily be out.

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Sen. Ted Cruz signalled that he would push the battle to the very end, meaning a batch of primaries on June 7 and then a possible floor fight at the July convention in Cleveland.

WATCH: Cruz, Sanders fight to stay in presidential race with Indiana primary win

0:53 Cruz, Sanders fight to stay in presidential race with Indiana primary win

But if he loses tonight, his prospects would rest on hope of some miraculous turnaround.

The reason Indiana is so important is because victory there would allow Trump to lose a number of other remaining states – Nebraska, Oregon, Washington, Montana and South Dakota – and still emerge victorious.

All he’d have to do is perform somewhere close to the polls in states where he’s expected to do better – like New Jersey and California

He’d be in a tougher spot without Indiana’s delegates. The state offers 57 – including 30 to whoever wins the popular vote. Most polls show Trump ahead.

READ MORE: Ted Cruz faces make-or-break moment to stop Donald Trump in crucial Indiana primary

The state is also a bit of a bellwether as it sits near the crossroads of two regions: the East, where Trump has dominated, and the Midwest, where he’s lost consistently.

Cruz says he’s staying in the race – no matter what.

“We are in for the distance,” he told reporters Monday. “We are competing – as long as we have a viable path to victory, I am in to the end.

“We’re headed to a contested convention. And at the contested convention, the battle is going to be who can earn the support of a majority of the delegates elected by the people.

VIDEO: ‘Even I would’ve helped her’: Trump reacts to Cruz not helping Fiorina following fall off stage

0:42 ‘Even I would’ve helped her’: Trump reacts to Cruz not helping Fiorina following fall off stage

“I’ll tell you, the reason Donald Trump is so desperate to get everyone to call this race over and the reason why so many of his media acolytes echo that sentiment, is that Donald knows that he cannot earn a majority at the convention of the delegates who’ve been elected by the people. And if you can’t earn a majority, you can’t be the nominee, because it means you can’t unite the party and you’d be an incredibly weak general election candidate.”

It’s true that Cruz has out-organized the frontrunner at certain state conventions that select delegates. That could allow him to overtake Trump on a hypothetical second or third ballot, as delegates would be unfettered by primary results and allowed to switch allegiances.

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But the momentum in the race hasn’t been on his side.

Widely considered the most detested member of Congress among his colleagues, Cruz has picked up only a few endorsements. The party machine, while fearful of Trump, hasn’t rallied around him either.

WATCH: Voters wait to see if Indiana decides presidential nominees

1:16 Voters wait to see if Indiana decides presidential nominees

And Trump has been on a tear, racking up bigger-than-expected wins in recent weeks.

“Indiana really is a must-win for Cruz in order to prevent Trump from winning on the first ballot,” said Kyle Kondik of Sabato’s Crystal Ball, a website run by University of Virginia’s Center for Politics.

“(Trump is) really only getting stronger. So I think it might be all over but the shoutin’ if Trump wins Indiana.”