It’s a rather remarkable phenomenon: The two front-runners are having trouble closing the deal.

By this point in the campaign, Donald Trump and Hillary Clinton should be thinking about running mates and planning for the fall. Instead, they both had their hands full trying to stave off defeat in Wisconsin.

And both campaigns, in an apparent sign of frustration, put out preemptive memos defending their positions against the press and the prognosticators.

Ted Cruz easily won Wisconsin yesterday, a symbolically important victory even though only 42 delegates were at stake. And Bernie Sanders romped in Wisconsin, with Fox calling the race as soon as the polls closed at 8 p.m. central.

Trump was on an incredible roll two weeks ago, having won 20 states and driven all but two rivals out of the race. Instead, Wisconsin gave a big psychological boost to Cruz, who captured his first major primary outside his home state of Texas.

But it’s important that the pundits not go overboard here. Trump is still going to the convention with a big lead, even if yesterday’s contest made it slightly harder for him to get to 1,237. Cruz has almost no hope of reaching the magic number and would have to win the nomination after the first ballot.

Many forces combined to deny Trump the win. The GOP establishment, in this case led by Scott Walker, did everything it could to derail him. He made a series of missteps, from abortion comments that ticked off the pro-life and pro-choice sides to retweeting an unflattering photo of Cruz’s wife. The press smelled blood in the water.

And maybe Wisconsin was never a great state for Trump. Although some areas have plenty of blue-collar workers, its voters are, on average, better educated and more religious than in most other states, and that isn’t The Donald’s base.

Little wonder, then, that Trump senior adviser Barry Bennett complained in a leaked memo that the “pathetic” and “idiotic” media were exaggerating the candidate’s problems.

Cruz also deserves credit for staying on message, garnering support from politicians who don’t much like him, and counterpunching without getting too personal (except for the “sniveling coward” moment).

Clinton’s loss is even more inexplicable. She has now been beaten in six out of seven contests by a 74-year-old self-proclaimed socialist who never should have been much of a rival.

The media have focused far less on the Democratic race because of a nearly universal conviction that Clinton, regardless of her stumbles, is a lock to win the nomination.

But strange things are happening. Bernie raised $15 million more than Hillary last month, and he hasn’t held a single fundraiser. Grass-roots liberals are filling his coffers, despite the widespread chatter that he will lose, while Hillary holds big-money events that further brand her as the candidate of the monied establishment.

Clinton campaign manager Robby Mook felt compelled to issue a pre-Wisconsin memo insisting that “Hillary Clinton has built a nearly insurmountable lead among both delegates and actual voters. Contrary to the claims of the Sanders campaign, in measure after measure, Clinton has shown the broadest support of any candidate currently running for president.”

And yesterday, when Sanders’ top aide told CNN his campaign would work on flipping superdelegates at the Philadelphia convention, Hillaryland sent out a blast saying he wants to overturn the will of the voters.

Wisconsin fit the Sanders formula, a predominantly white state with a strong progressive tradition. But he is the one generating the big crowds and excitement, while she increasingly sounds like the Hillary of 2008, promising sensible change and scoffing at the inspirational rhetoric of her opponent.

Oddly enough, the Sanders team conceded in a lengthy New York Times piece that had the senator been more aggressive against Clinton in 2015 and spent more time on the trail, he might be well positioned now to win. Although Hillary might have responded in kind if Sanders had whacked her over the email scandal and other matters, the story read like a post-mortem reflection on defeat.

So how is it that Trump and Clinton have hit this rough patch?

They could not be more different. Trump is the bombastic outsider with no political experience, Clinton the consummate insider since her days as first lady.

Trump mostly wings it; Clinton speaks in position-paper paragraphs. Trump is entertaining; Clinton, who says she’s not a natural politician, can be dull. He speaks the language of a native New Yorker; she sounds like a former New York senator.

Clinton met with world leaders as a globe-trotting diplomat; Trump has built hotels and golf courses around the world.

But they share one thing in common: high negatives. They would, according to current polls, be the most unpopular major-party nominees in memory. Trump has high unfavorable ratings from women; Clinton, despite her gender advantage, has had trouble winning over younger women.

And that, in a nutshell, is why neither one has been able to wrap things up.