Republican front-runner Donald Trump has said he would easily win the Republican nomination if John Kasich drops out of the contest.
He said the Ohio governor should not stay in the contest because he cannot collect enough delegates to win.
His comments came just ahead of Tuesday's Wisconsin vote which could reshape the Republican race.
"If I didn't have Kasich, I automatically win," Mr Trump said at a rally in Wisconsin.
If Mr Trump loses the primary contest on Tuesday, as the polls suggest, it is far less likely he will have the all-important 1,237 delegates needed to secure the nomination.
Delegates represent their states at the party's convention and are accumulated by the votes in each state.
Currently, Mr Trump has 735 delegates, Texas Senator Ted Cruz 461 and Ohio Governor Mr Kasich 143.
If no-one hits 1,237 after all 50 states have voted, the Republican convention in July is contested, meaning the delegates vote for a nominee, and Mr Trump, who is unpopular among sections of the party, could lose the nomination.
The New York businessman has had a very difficult seven days, sparking outcry over comments he made about abortion, standing by his campaign manager after he was charged with assaulting a reporter and raising eyebrows with remarks about US foreign policy.
"Was this my best week? I guess not," Mr Trump told "Fox News Sunday".
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A loss in Wisconsin, which is the kind of state he has done well in up to now, then questions will be raised about whether his campaign is running out of steam.
He met the Republican National Committee (RNC) in Washington to review delegate and party rules, days after breaking a promise made to them that he would back the eventual nominee.
In response to Mr Trump's comments that Mr Kasich should follow former Florida Governor Jeb Bush and Florida Senator Marco Rubio and quit the race, the Ohio Governor said he will stay because no-one will get the required number to win outright.
"Since he thinks it's such a good idea, we look forward to Trump dropping out before the convention," Kasich spokesman Chris Schrimpf said.
Mr Kasich has recognised that he will not be able to gain enough delegates before the convention.
Reince Priebus, president of the RNC, has said the nominee will be someone who is running, but acknowledged that a brokered convention is a possibility.
The Democrats are campaigning ahead of Wisconsin's primary as well, where Hillary Clinton is hoping to hold off a resurgent Bernie Sanders.