US presidential primaries spark back to life Tuesday after an eventful 10-day break with clear frontrunners Donald Trump and Hillary Clinton both facing the real possibility of losing in Wisconsin.
Defeat in the north-central state isn't likely to immediately change the course of the overall nominating contest, but it could serve as an indicator of the race's current status ahead of the New York primary on April 19, where polls show both in the lead.
It's been a bumpy period for Trump, the Republican billionaire from New York. Although his campaign has seemed bullet-proof up until now, his latest controversies - including abortion, opponent Ted Cruz's wife and a journalist who said she was roughed up by Trump's campaign manager - have alienated women voters further, polls indicate.
His divisive style is also under scrutiny, and the real estate magnate had a surprise meeting with Republican party chief Reince Priebus in Washington on Thursday amid rumblings that the party would fracture if he were to win the nomination.
With polls for the Wisconsin Republican primary showing the ultraconservative Cruz holding a 10-point lead, Trump has launched a series of events in the heartland state to rally support. Moderate John Kasich, the Ohio governor, is polling third and last.
Campaigning in Wisconsin on Saturday accompanied by Sarah Palin, Trump attacked Cruz for failing to report a loan from Goldman Sachs, his wife's employer.
And on Sunday, Trump doubled down on some of his more controversial assertions in recent days - that the United States should consider leaving Nato and that Japan should be responsible for its own nuclear defence.
"Sometime you're better off saying, wait a minute. We're defending Japan. I mean what we're doing is costing us a fortune," he told the Fox News Sunday program.
"And not only Japan, (but) South Korea. We have 28,000 soldiers on the line," said Trump, who said that rather than fully reimbursing the US for their defence "they pay us peanuts."
He added: "Maybe they would, in fact, be better off if they defend themselves from North Korea... including with nukes."
The winner of Tuesday's Republican primary will take most of the 42 delegates on offer. If Cruz wins, he will certainly claim it as a turning point in the race, but mathematically speaking he will struggle to overcome his overall delegate deficit.
Currently, Trump has 739, Cruz 460 and Kasich 145. To win the Republican nomination outright, a candidate needs 1,237.
In North Dakota, Republican activists gather this weekend at a state convention to select 25 of 28 delegates, but unlike those from most other states, they won't be bound to a particular candidate at the party's convention in July. The other three are RNC members who are automatic delegates.
For Clinton, a loss in Wisconsin would be more symbolic than anything else, as the state distributes delegates proportionally according to the primary results.
But she comes into the contest having lost five of the last six states to Bernie Sanders, and polls show him finishing on top in Wisconsin.
The Vermont senator has already notched victories in two neighbouring states, Minnesota and Michigan, and his popularity is undeniable in Wisconsin cities like Madison, which have a high concentration of university students.