Donald Trump fights for Wisconsin votes after difficult week

A frustrated Donald Trump stepped up his presidential campaign after a rough week and found himself on the defensive just two days before the closely watched primary in Wisconsin.

The billionaire tycoon faces the prospect of a loss that could stem his momentum towards securing the Republican nomination, as he trails Texas senator Ted Cruz in the polls in Wisconsin.

He was trying to recover from a week in which he found himself struggling to explain away controversies over abortion, nuclear weapons and his campaign manager.

"Was this my best week? I guess not," Mr Trump said on Fox News Sunday.

Defeat in Tuesday's primary will raise doubts that the real estate mogul can net the needed delegates to win the nomination outright, making it far easier for his party to oust him at the Republican national convention in Cleveland in July.

Mr Trump urged John Kasich to drop out of the race, arguing that the Ohio governor, who has only won his home state so far, should not be allowed to continue accumulating delegates if he has no chance of being the nominee.

He suggested that Mr Kasich, who has pledged to make it to the summer convention, follow the example of Florida senator Marco Rubio and former Florida governor, Jeb Bush - candidates who quit after lagging behind.

"He doesn't have to run and take my votes," Mr Trump said.

Mr Kasich's campaign argued that neither Mr Trump nor Mr Cruz would have enough delegates to win the nomination outright going into the convention.

"Since he thinks it's such a good idea, we look forward to Trump dropping out before the convention," said Kasich spokesman Chris Schrimpf.

On the Democratic side, Hillary Clinton said she had yet to receive a request from the FBI for an interview regarding the private email system she used as secretary of state.

And she got in a dig at her Democratic opponent, Vermont senator Bernie Sanders, who has identified as an independent for most of his career.

"I know we have to have a Democrat succeed Barack Obama," Mrs Clinton said.

The two candidates have agreed to a debate in New York before the key April 19 primary, though the timing remained unclear.

Mr Sanders fired up a crowd in Wausau, Wisconsin, hoping to continue his string of recent campaign victories even as Mrs Clinton maintains a big lead in delegates to the party's national nominating convention in July in Philadelphia.