"Last night was Donald Trump's night, and today is Indiana's day," Cruz told reporters in Indianapolis on Wednesday morning. 
Cruz said he would make his "major announcement" at 4 p.m. EDT during his Indiana rally but refused to say what it would be about. 
Indiana Gov. Mike Pence has yet to endorse a candidate in the GOP presidential race, and speculation persists that he may lend his support to Cruz.
Cruz and Trump, the party's front-runner, have both met privately with Pence, though Trump said Wednesday morning on CNN's "New Day" that he did not think "anyone else" would get the governor's endorsement.
"He may not endorse, I don't think he'll endorse anybody actually, and he may endorse us, I don't know," Trump said, describing the governor as a "great guy" and praising his tenure in Indiana.
And reports this week said Cruz has been vetting Carly Fiorina as a potential running mate and even that he could announce a running mate during the primary.
Cruz is competing for momentum against Trump, who held a round of television interviews Wednesday morning and has planned his first major foreign policy address Wednesday at the Mayflower Hotel in Washington, D.C.
Cruz sought to preemptively blunt Trump's speech, going after his positions on Israel and the Iran nuclear deal and characterizing them as in line with those of Democratic presidential front-runner Hillary ClintonHillary Diane Rodham ClintonRepublican Ohio Senate candidate slams JD Vance over previous Trump comments Budowsky: Why GOP donors flock to Manchin and Sinema Countering the ongoing Republican delusion MORE.
"It will be interesting to see what Donald says in his foreign policy speech, whether he highlights the fact that Donald and Hillary both agree that America should be neutral between Israel and the Palestinians," Cruz told reporters. 
"Donald Trump and Hillary Clinton also both agree that the Iranian nuclear deal should stay in place. That is a profoundly dangerous left-wing position of Donald Trump," Cruz argued.
"Maybe he'll make it great," Cruz said, mocking Trump's vow to renegotiate the nuclear deal.
Cruz and fellow candidate John Kasich are trying to deny Trump the 1,237 delegates needed to lock up the GOP nomination, forcing a contested Republican National Convention in July. 
Trump’s series of wins Tuesday night makes it tougher to stop him. Anti-Trump forces are looking to next week’s Indiana primary as a chance to strike a blow against the front-runner.
Updated at 10:35 a.m.