WASHINGTON — Despite pinning his presidential hopes on Indiana, Ted Cruz is down 15 points in that state, a new poll revealed Sunday.

The NBC News/Wall Street Journal/Marist poll shows Donald Trump dominating, receiving the support of 49 percent of likely Republican primary voters, with Cruz at 34 percent and Gov. John Kasich is at 13 percent.

“It’s over,” Trump declared on Fox News Sunday if he wins Indiana Tuesday. “I think it’s over now. But it’s over. Cruz cannot win. Cruz cannot win. He’s got no highway.”

The poll shows a backfiring of a pact the Texas senator forged with Kasich to campaign alone in Indiana, while leaving New Mexico and Oregon to Kasich.

The majority of likely GOP voters (58 percent) said they disagree with the stop-Trump deal, while just 34 percent approve.

Cruz has framed Indiana as an “absolutely pivotal” last stand and won the support of Gov. Mike Pence and even named Carly Fiorina as running mate to gin up excitement for his campaign.

Already mathematically impossible for him to win the nomination before the convention, Cruz said he’ll still stick around even he loses Tuesday.

“I agree that Indiana is incredibly important,” Cruz told Fox News Sunday. “Regardless of what happens in Indiana, Donald Trump is not getting to 1,237 (delegates for the nomination). No one’s getting to 1,237. We are heading to a contested convention.”

Cruz had one major flub while trying to recreate a famed scene from the movie “Hoosiers,” Cruz called a hoop a “basketball ring” in the famous gym. President Obama even roasted Cruz for the slip at Saturday’s White House Correspondents Association dinner: “What else is in his lexicon? Baseball sticks? Football hats? But sure, I’m the foreign one.”

Trump has 996 delegates, compared to Cruz’s 565 and Kasich’s 153 delegates. There’s 57 delegates of up for grabs in Indiana.

“In Indiana, Trump is positioned to corral all the [state’s 57] delegates, which will be a big prize toward winning the nomination outright,” Lee Miringoff, director of the Marist College Institute for Public Opinion, told NBC News. “Clinton and Sanders are more likely to divide the delegate pool, which will do little to change the narrative on the Democratic side.”

Buoyed by the endorsement of basketball coaching legend Bobby Knight, Trump hopes a victory in Indiana Tuesday will be a game changer and help him avoid a contested convention in July by winning the necessary delegates outright in the remaining states.

In more good news for Trump, Indiana voters pick the New York billionaire over Clinton in a hypothetical match-up 48 percent to 41 percent. Cruz also has a seven-point advantage over Clinton (50-43 percent), undercutting his argument he’s the only candidate who can beat the former Secretary of State.

On the Democratic side, Hillary Clinton has a narrow lead over Bernie Sanders: 50 percent to 46 percent in Indiana, the poll showed. But a close outcome on Tuesday should do little to change the wide delegate lead she holds over Sanders: 2,165 delegates to his 1,357.

Sanders does better against the GOP contenders than Clinton in Indiana. Trump beats Sanders 47 to 46 percent, whereas Sanders beats Cruz by three points 48-45 percent.