Republican presidential hopeful Ted Cruz Rafael (Ted) Edward CruzSenate Republicans face tough decision on replacing Ginsburg Cruz: Trump should nominate a Supreme Court justice next week Renewed focus on Trump's Supreme Court list after Ginsburg's death MORE said on Sunday he would continue his campaign if he lost the critical Indiana primary on Tuesday.

"If you don't win in Indiana under these circumstances, is this race over?" asked "Fox News Sunday" host Chris Wallace.

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"Of course not," Cruz said. "It's going to be a battle to see who can earn a majority of the delegates elected by the people at the convention. And the reason Donald is so frantic to say the race is over ... is because Donald knows he cannot earn a majority of the delegates that were elected by the people.

"I agree that Indiana is incredibly important," Cruz added.

Cruz in the days leading up to the primary has announced former Hewlett-Packard CEO Carly Fiorina as his running mate and gained the endorsement of Indiana Gov. Mike Pence (R).

He also cut a deal with rival Ohio Gov. John Kasich in the hopes of boosting his chances in the Hoosier State. In exchange for Kasich pulling out of Indiana, thus helping Cruz gain more support in the state, the Texas senator would forgo campaigning in New Mexico and Oregon to pave the way for Kasich to best Trump in those states. The deal was struck in an attempt to stop Trump from securing the GOP nomination.

However, an NBC News/Wall Street Journal/Marist poll released Sunday shows Trump with a 15-point lead over Cruz in the state, with 49 percent support among likely Republican primary voters.

Indiana's May 3 primary offers up 57 delegates.

Cruz believes none of the candidates will earn the 1,237 delegates necessary to clinch the GOP nomination in the primary process, which would force a contested Republican National Convention in July.

However, Trump has inched closer to that requirement and continues to say he will clinch after predicted big wins in Indiana and California.

Trump has 996 delegates to Cruz's 565, according to The Associated Press delegate tracker. Kasich has 153.