One would be forgiven for thinking that given the intensity of the Republican race, Donald Trump and Ted Cruz would made sensible use of their evenings by getting some rest.
But as a new poll showed the contest getting even tighter, the two choose to engage in a late night Twitter row, as the mud-slinging and insults – which has now dragged in their wives – increased.
The row has it origins in a campaign advert produced by an anti-Trump group not linked to Mr Cruz, which featured an image of the tycoon’s wife from a 2000 model shoot for GQ magazine. Mr Trump had accused Mr Cruz of being involved in the advert and warned that he would “spill the beans” about the senator’s wife, Heidi.
On Wednesday evening, Mr Trump retweeted an unflattering image of Mrs Cruz alongside an image of his wife, Melania.
Mr Cruz responded by tweeting: “Donald, real men don't attack women. Your wife is lovely, and Heidi is the love of my life.”
Earlier in the day, the Texas senator had told CNN: “If Donald wants to get in a character fight he’s better off sticking with me, because Heidi is way out of his league.”
Mr Trump accused Mr Cruz of stealing the line from Michael Douglas as the star of the 1995 movie The President.
“Lyin’ Ted Cruz steals foreign policy from me, and lines from Michael Douglas - just another dishonest politician,” Mr Trump tweeted.
In the film, the character played by Douglas says - referring to his girlfriend: “If you want a character debate Bob, you better stick with me because Sydney Ellen Waid is way out of your league.”
The advertisement featuring the glamour shot of Mrs Trump was produced by an anti-Trump super PAC, Make America Awesome, which has no known connection to the Cruz campaign, but which urged voters in Utah to vote for the Texas senator.
Mr Cruz won the Republican contest in Utah Tuesday, capturing more than 50 per cent of the vote and all 40 of the state’s delegates. Mr Trump won the night's Arizona primary.
Donald Trump's most controversial quotes
Donald Trump's most controversial quotes
1/14 On Isis:
"Some of the candidates, they went in and didn’t know the air conditioner didn’t work and sweated like dogs, and they didn’t know the room was too big because they didn’t have anybody there. How are they going to beat ISIS?"
2/14 On immigration:
"I will build a great wall — and nobody builds walls better than me, believe me —and I’ll build them very inexpensively. I will build a great, great wall on our southern border, and I will make Mexico pay for that wall. Mark my words."
3/14 On Free Trade:
"Free trade is terrible. Free trade can be wonderful if you have smart people. But we have stupid people."
PAUL J. RICHARDS | AFP | Getty Images
4/14 On Mexicans:
"When Mexico sends its people, they’re not sending their best. They’re sending people that have lots of problems. They’re bringing drugs. They’re bringing crime. They’re rapists."
5/14 On China:
"I just sold an apartment for $15 million to somebody from China. Am I supposed to dislike them?... I love China. The biggest bank in the world is from China. You know where their United States headquarters is located? In this building, in Trump Tower."
6/14 On work:
"If you're interested in 'balancing' work and pleasure, stop trying to balance them. Instead make your work more pleasurable."
7/14 On success:
"What separates the winners from the losers is how a person reacts to each new twist of fate."
8/14 On life:
"Everything in life is luck."
9/14 On ambition:
"You have to think anyway, so why not think big?"
10/14 On his opponents:
"Bush is totally in favour of Common Core. I don't see how he can possibly get the nomination. He's weak on immigration. He's in favour of Common Core. How the hell can you vote for this guy? You just can't do it."
11/14 On Obamacare:
"You have to be hit by a tractor, literally, a tractor, to use it, because the deductibles are so high. It's virtually useless. And remember the $5 billion web site?... I have so many web sites, I have them all over the place. I hire people, they do a web site. It costs me $3."
12/14 On Barack Obama:
"Obama is going to be out playing golf. He might be on one of my courses. I would invite him. I have the best courses in the world. I have one right next to the White House."
13/14 On himself:
"Love him or hate him, Trump is a man who is certain about what he wants and sets out to get it, no holds barred. Women find his power almost as much of a turn-on as his money."
14/14 On America:
"The American Dream is dead. But if I get elected president I will bring it back bigger and better and stronger than ever before and we will make America great again."
“When Donald gets scared, when he gets angry, when he gets threatened ... So last night Donald threatened my wife, he went directly after my wife,” Mr Cruz said. He said Mr Trump was engaging in "gutter politics".
Mrs Cruz is a senior executive for Goldman Sachs, and took a leave from work in order to help her husband's campaign. She has become one of the campaign's most accomplished fundraisers.
Mrs Cruz also defended herself against Mr Trump, saying: “We are not worried in the least. I have one job in this campaign and that is to help Ted win this race. I think it is the easiest job in the world.
“All I have to do is speak the truth about what I know about my husband and our family.”
The spat came as a new poll from Fox News found that Mr Cruz and John Kasich are ahead of Hillary Clinton in one-on-one match-ups, but Mr Trump trails the Democratic front runner by 11 points.
The poll said Mr Kasich was the Republican's best shot of beating Ms Clinton, In a national poll of the Republicans, Mr Trump remains in the top spot with 41 per cent support, while Mr Cruz has 38 per cent. Mr Kasich gets 17 per cent.