Donald Trump has insisted the Republican nomination race "is over" if he wins in Indiana next week.
But speaking in Evansville in the hotly-contested state, he continued to rail against what he calls the "crooked way" the party picks its nominee and claimed his rival Ted Cruz is unfairly winning delegates.
Read more: Trump accuses Clinton of 'playing the women' card
The Republican front-runner said Mr Cruz "can only successfully win support by wooing delegates with steaks and trips".
Mr Trump then said the winner "should be based on votes, not on whether people like a certain steak from a certain place".
Mr Cruz, meanwhile, has claimed one of his critics let his "inner Trump come out" when he described the Texan as "Lucifer in the flesh".
As he campaigned ahead of the Indiana Republican primary on Tuesday, Mr Cruz took issue with former House speaker John Boehner's barb.
Mr Boehner told a Stanford University audience this week that he has "never worked with a more miserable son of a bitch in my life" than Mr Cruz.
Mr Cruz said he never actually worked with Mr Boehner, and the White House candidate said he would be surprised if the two politicians ever exchanged more than 50 words.
And Mr Cruz had this message for voters: "When John Boehner calls me Lucifer, he's not directing that at me. He's directing that at you."
Mr Boehner resigned last autumn under pressure from conservatives allied with Mr Cruz. His well-known contempt for the Texan stems in part from Mr Cruz's role forcing a partial government shut-down in 2013.
Mr Boehner said he and Mr Trump are "texting buddies" and he will vote for the property tycoon.
Elsewhere, Mr Cruz's running mate Carly Fiorina attempted to explain the rules of the Republican Party to rival Mr Trump as she looked to assert why the race for the nomination could go to a contested convention.
In an interview on MSNBC's Morning Joe, Ms Fiorina said Mr Trump will get "shellacked by Hillary Clinton" if he is the nominee for the Republican Party, but asserted that he could lose the nomination if he does not get the majority.
"Donald Trump just figured it out, but wow, this system has been in place for a very long time," she said, referring to his claims that he should be named the nominee even if he falls slightly short of the required 1,237 delegates needed to win the nomination.
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