Republican presidential candidate Ted Cruz speaks in Oshkosh, Wis. on Friday. (Mark Kauzlarich/Reuters)

On Friday, Sen. Ted Cruz denied a National Enquirer story alleging that he participated in at least five extramarital affairs.

“This National Enquirer story is garbage,” the Texas Republican said after an event in Wisconsin. “It is a tabloid smear.”

He went on to blame Donald Trump for planting the story in the Enquirer. (Trump and the chief executive of the National Enquirer’s publisher are close and longtime friends.) Cruz also posted a response on his Facebook page that read in part: “Donald Trump’s consistently disgraceful behavior is beneath the office we are seeking and we are not going to follow.”

Trump’s response was absolutely, well, Trumpian. “Ted Cruz’s problem with the National Enquirer is his and his alone,” Trump said in a statement on Facebook, “and while they were right about O.J. Simpson, John Edwards, and many others, I certainly hope they are not right about Lyin’ Ted Cruz.”

The denial of an affair allegation published in the National Enquirer and all that followed is, in many ways, the most fitting possible end to what is unquestionably the worst week of the Republican race. And given where the race has gone before, that’s saying something.

Republican presidential candidate Donald Trump speaks on March 21 in Washington. (Evan Vucci/AP)

This was a week in which an anti-Trump super PAC published a near-nude picture of Trump’s wife, Melania, in hopes of turning Utah voters off the real estate mogul before that state’s primary last week. Trump — Donald, not Melania — responded, of course, via Twitter with an insinuation that Cruz’s wife, Heidi, had a secret about which he would “spill the beans.”

Heidi Cruz was forced to respond, saying she didn’t have a secret. Then Trump retweeted an image featuring a less-than-flattering picture of her next to a glamorous one of Melania Trump. The images bore this caption: “No need to ‘spill the beans.’ The images are worth a thousand words.”

Just in case you may have forgotten, this is not a race for junior high school class representative. One of these two men has a high chance of being the Republican nominee for president. A very high chance.

Although the reaction to the Cruz allegations and Trump’s don’t-blame-me response tended toward surprise and disgust, neither feeling makes much sense when you consider the context of the broader campaign.

Trump has proved time and again that there are no limits to what he will say, allege or hint at when it comes to his political opponents and their families. Remember that Trump retweeted (and then deleted) a post that read “#JebBush has to like the Mexican Illegals because of his wife.” Trump subsequently said he didn’t regret the tweet and refused to apologize to the former Florida governor or his wife for it.

Trump attacked Sen. Marco Rubio of Florida as sweaty. He went after Bush as “low energy.” He has repeatedly called Cruz a liar. Trump has talked about the size of his hands and, by association, his genitals. And those are just the ones I can remember off the top of my head.

Trump is going to do Trump. The problem comes when other candidates — or their aligned groups — conclude that the best way to slow or stop Trump is to try to out-Trump him. Never works.

Republican frontrunners Ted Cruz and Donald Trump exchange jabs on Sunday talkshows over a National Enquirer article alleging extramarital affairs by Cruz and a near nude photo of Trump's wife distributed by an anti-Trump super PAC. (The Washington Post)

Rubio spent several days earlier this month in the gutter with Trump, slamming his looks, his bathroom habits and, yes, his hand size. It totally backfired. People expected such comments from Trump. Coming from Rubio, the attacks felt vulgar and off. He was out of the race within days.

Then the anti-Trump group went there with the picture of Melania, touching off another cycle of lowest-common-denominator politics that winds up splashing mud everywhere.

This is the campaign that Trump wants: chaos, unpredictability, un-seriousness.

During a week in which 31 people died and hundreds more were wounded in another major terrorist attack in Europe, the Republican race was about “spill the beans,” almost-nude photos and alleged affairs first published in a gossip rag. Ask yourself which of the remaining three GOP candidates — Trump, Cruz or Gov. John Kasich of Ohio — will prosper, or at least not be damaged, by that prurient focus. The answer is obvious.

The past seven days highlight what this campaign season has become. An absurd race to the bottom in which the debate is about who is losing less badly and where winners are impossible to find. We — and the GOP field — know exactly how we got here. I’m just not sure anyone knows how we can escape.