Here are six times Republican presidential contender Donald Trump has insulted women, from Rosie O'Donnell to Ted Cruz's wife, Heidi. (Sarah Parnass and Nicki DeMarco/The Washington Post)

Late Wednesday night, Republican presidential front-runner Donald Trump retweeted a side-by-side photo comparison of his wife, Melania Trump, and Heidi Cruz, the wife of Trump's chief rival, Sen. Ted Cruz (R-Tex.). Written on the photo in white lettering: "No need to spill the beans" and "The images are worth a thousand words."

Within the hour, Cruz responded on Twitter: "Donald, real men don't attack women. Your wife is lovely, and Heidi is the love of my life."

How in the world did we get to this point? Here's a timeline:

Melania Trump, wife of Republican U.S. presidential candidate Donald Trump, talks to the media as she visits the "spin room" with her husband after the conclusion of the Republican U.S. presidential candidates debate sponsored by CNN at the University of Miami in Miami, Florida March 10, 2016. REUTERS/Joe Skipper Melania Trump, wife of Donald Trump, talks to the media earlier this month in Miami. (Reuters/Joe Skipper)

Earlier this week: Ahead of the Utah Republican caucuses, the anti-trump super PAC Make America Awesome targeted Mormon voters with a series of Facebook ads, including one that features a seemingly nude photo of Trump's wife, Melania, during a modeling shoot for GQ magazine more than 15 years ago. On the photo is this message: "Meet Melania Trump, your next first lady. Or, you could support Ted Cruz on Tuesday."

Make America Awesome was started by GOP strategist Liz Mair, who previously worked for Mitt Romney, Wisconsin Gov. Scott Walker and Carly Fiorina. Unlike some super PACs that are flush with millions of dollars, Make America Awesome has limited funds and has mostly invested in low-budget social media ads and radio. Super PACs are forbidden from coordinating with candidates, and unlike many other super PACs, Make America Awesome was formed to hurt Trump's candidacy rather than to help a particular presidential candidate.

Tuesday night: Minutes before the scheduled start of the caucuses, Trump tweeted: "Lyin' Ted Cruz just used a picture of Melania from a G.Q. shoot in his ad. Be careful, Lyin' Ted, or I will spill the beans on your wife!" Keep in mind, this tweet landed on the same day that the world was reeling from the terrorist attack in Brussels that killed at least 34 people and shifted media attention away from the presidential election.

Later in the evening, Cruz responded on Twitter: "Pic of your wife not from us. Donald, if you try to attack Heidi, you're more of a coward than I thought."

Wednesday morning: In an interview with the "Today" show, Cruz called Trump "a bully" and theorized that his rival's threatened attack stemmed from unhappiness that "he got clobbered in Utah," losing the state to Cruz. He again warned Trump not to attack Heidi Cruz, adding: "Donald is a bully." And he insisted that he had nothing to do with the super PAC's ad.

But Trump continued to insist that Cruz did have something to do with the ads, tweeting: "Lyin' Ted Cruz denied that he had anything to do with the G.Q. model photo post of Melania. That's why we call him Lyin' Ted!"

Heidi Cruz spoke with a small group of reporters at her husband's campaign headquarters in Wisconsin and said that “in no way, shape or form" was her husband's campaign involved with the ad. When asked specifically about Trump's tweet the night before, Heidi Cruz said:  “You probably know by now that most of the things Donald Trump says have no basis in reality."

Later, Stephen Miller, a senior adviser to Trump, appeared on CNN and was asked what "beans" Trump was threatening to spill. Miller said that he was not in a position to say, but he said that his boss's "whole point was that we have to be careful not to go in that direction.” Miller called on Cruz to publicly condemn the super PAC. “We’re hoping that Ted Cruz is going to tell his super PACs to stand down," Miller said. "This is not a story about Donald Trump. This is a story about Ted Cruz and dirty, special interest money.”

Wednesday afternoon: Cruz continued to defend his wife and criticize Trump in an interview on the Fox Business Channel and in talking with reporters in New York. On television, Cruz seemed to adapt a famous line from the 1995 movie "The American President" as he said: "Donald Trump, if you want a character fight, stick with me because Heidi is way out of your league." Cruz later told reporters that his wife is "used to the rough and tumble" and "dealing with bullies," thanks to her corporate career. (Heidi Cruz in an investment manager at Goldman Sachs.)

Wednesday evening: Trump then went on the Fox Business Channel and defended his wife, a former model, and accused Cruz of "knowingly" circulating the GQ photo in Utah ahead of the caucuses. Trump said that Melania Trump is "very smart" and would be "a great first lady." He also explained that the photo first appeared in "GQ magazine, which is a very mainstream, nice magazine, it's a good magazine."

"As a model, she did shoots, and like all of the models they do, that's what they do. I mean, it's one of those things," Trump said. "And it was framed in such a way like it was really a terrible thing, and it was sent to a certain group, and I thought it was disgraceful. And Ted Cruz knew better."

Trump also explained the thinking behind his original tweet: "I wrote and said: Be careful because otherwise I'll have to start talking about your situation. Now, do I like doing that? No."

Late Wednesday night: Just before midnight, Trump retweeted the side-by-side photo comparison of his wife and Heidi Cruz.

About 35 minutes later, Cruz responded on Twitter: "Donald, real men don't attack women. Your wife is lovely, and Heidi is the love of my life."

Thursday morning: Sen. Lindsey Graham (R-S.C.) appeared on the "Today" show and urged both candidates to "knock this crap off because these are serious times, and you're not behaving like you want to be president of the United States." Graham, who has begrudgingly endorsed Cruz, said the back-and-forth bickering reminds him of a reality television show instead of a presidential race.

"It's a good year to be single," Graham said. "The bottom line is when you think it can't get worse, hey guys, knock it off. The world is falling apart. Man up. You've got great wives and great families."