Republican presidential front-runner Donald Trump is calling on rival John Kasich to get out of the White House race, arguing that the Ohio governor should not be allowed to collect future delegates because the nomination is already beyond his grasp.
Trying hard to get back on track after a difficult week, Mr Trump said it was unfair for Mr Kasich, the winner of only his home state's primary, to continue campaigning.
He suggested that Mr Kasich, who has pledged to make it to the summer convention, follow the lead of former candidates Marco Rubio and Jeb Bush - and quit.
"If I didn't have Kasich, I automatically win," Mr Trump said on the campaign trail in West Allis, Wisconsin, on Sunday evening.
Mr Trump said Mr Kasich could ask to be considered at the GOP convention in Cleveland in July even without competing in the remaining nominating contests. He said earlier on Sunday that he had shared his concerns with Republican National Committee officials at a meeting in Washington in the last week.
Mr Kasich's campaign countered that neither Mr Trump nor Texas Senator Ted Cruz would have enough delegates to win the nomination outright in Cleveland.
"Since he thinks it's such a good idea, we look forward to Trump dropping out before the convention," said Kasich spokesman Chris Schrimpf.
Across the political aisle, Democrat Hillary Clinton told NBC's Meet The Press that the FBI had yet to request an interview regarding the private email server she used as secretary of state.
Mrs Clinton and her Democratic opponent, Vermont Senator Bernie Sanders, announced that they had agreed to debate in New York before the important April 19 primary, though their campaigns continued debating over when to schedule the face-off.
Mr Sanders, meanwhile, fired up a crowd in Wausau, Wisconsin, hoping to continue a string of recent campaign victories even as Mrs Clinton maintains a sizeable delegate lead.
Mr Trump's call for Mr Kasich to bow out came as Republican concerns grew about the prospect of convention chaos if Mr Trump fails to seal his party's nomination - or even if he does.
Behind Mr Cruz in the polls in Wisconsin, Mr Trump faces the prospect that a loss on Tuesday there will raise further doubts that he can net the necessary number of delegates, making it far easier for his party to oust him in a floor fight at the convention in Cleveland in July.
Mr Cruz, Mr Trump's closest challenger, has only a small chance to overtake the real estate mogul in the delegate hunt before the convention. Mr Cruz spent Sunday rallying supporters, including conservative Wisconsin talk radio hosts who oppose Mr Trump's candidacy.
Mr Kasich acknowledges that he cannot catch up in the delegate race, leaving a contested convention his only path to victory. He has faced calls in the past to step aside, but those nudges became less frequent following his decisive victory last month in his home state.
Nevertheless, Mr Kasich has suggested that a contested convention would not involve the chaos that party leaders fear.
"Kids will spend less time focusing on Bieber and Kardashian and more time focusing on how we elect presidents," he told ABC. "It will be so cool."
Republicans fear a bruising internal fight would damage the party in November's general election. Mr Trump is also not ruling out the possibility of running as an independent if he is not the nominee, making it that much harder for the GOP to retake the White House.
Such talk has "consequences", said GOP chairman Reince Priebus, though he tried to quell the prospect of a convention fight. He told ABC that the process will be clear and open, with cameras there "at every step of the way".
Frustration with the GOP field has stoked calls in some Republican corners for the party to use a contested convention to pick someone not even on the ballot. Mr Priebus acknowledged that was a remote possibility, but said he believed his party's nominee would be "someone who's running".
Mr Trump has been on the defensive as he struggled to explain away a week of controversies over abortion, nuclear weapons and his campaign manager.
"Was this my best week? I guess not," he told Fox News Sunday.