The second week of October is likely to be remembered as the moment when the 2016 presidential campaign went careening off the rails and spinning into the void.

Pundits and election wags love to talk about the so-called "October surprise" - a last-minute revelation that turns an election upside down. This October, the only surprise seems to be a day without surprises.

Here are just some of the highlights of a week that will likely cast a shadow over US politics for years to come.

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Sunday night mud-wrestling

If there were any doubts about the direction the second US presidential debate was going to take on Sunday night, they were dispelled an hour before showtime, when Donald Trump held an impromptu press conference with women who have accused Bill Clinton of sexual assault.

The striking thing is that while the former president's sexual history was broached by the Republican, it probably wasn't the most eye-popping, norm-breaking moment of the debate.

That, instead, came when Mr Trump said that Hillary Clinton feared his presidency because his election would lead to her imprisonment.

"Such incendiary talk is an affront to elementary democratic decency and a breach of the boundaries of American political discourse," writes conservative columnist Charles Krauthammer.

In the days since the debate, Mr Trump has only increased the voltage. Where once he used to downplay his crowd's "lock her up" chants, now he eggs them on.

"She has to go to jail," he said at a Pennsylvania rally.

Gone is any semblance of moderation or talk of pivot and restraint. It's red meat from here on out.

Media playback is unsupported on your device Media caption Apprentice contestant Summer Zervos accuses Donald Trump of 'thrusting his genitals' at her during a business meeting

Parade of the accusers

While Mr Trump's embrace of "lock her up" rhetoric received the lion's share of condemnation from the left and the right, that debate moment likely won't have the greatest impact on the final month of the campaign. That (dubious) honour goes to his assertion that his secretly recorded discussion of how he made unwelcome advances on women was "just talk".

Such a blanket denial has prompted a steady stream of women to come forward to assert that Mr Trump's actions do, in fact, reflect his candid words. Jessica Leeds, who accused Mr Trump of fondling her on a plane, said she practically jumped out of her skin when she heard Mr Trump deny any improper behaviour.

The Trump campaign has promised that it will release evidence that the accusers are fabricating their claims - and Mr Trump in several speeches has issued blanket denials. So far, however, the sum total of evidence levelled against the growing list of women coming forward is a discussion of the mobility of airline armrests, an insistence that Mr Trump wouldn't have enough private time with the women in question to do anything untoward and, most amazingly, Mr Trump's own assertion that one of the women wasn't attractive enough to catch his eye.

"Believe me, she would not be my first choice," he said at a North Carolina rally on Friday.

Believe me, that line isn't going to win him any votes.

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Hacked to pieces

You'd be hard-pressed to notice over the din of the travelling circus the Trump campaign has become, but the Clinton team also spent the week weathering a scandal of its own. Thanks to the release by Wikileaks of emails possibly acquired by Russian hackers, the public has been given an inside view of the Clinton campaign - and the picture it paints is often unflattering.

Campaign operatives obsess over messaging and even individual tweets, they mull over negative campaign tactics, try to resolve staff infighting and speculate on ways to inspire a liberal revolt within the Catholic Church.

The emails - assuming they are authentic - contain a full opposition-research dossier on primary opponent Bernie Sanders and staff-culled highlights of the most controversial portions of Mrs Clinton's speech to Wall Street banks that feature her pining for a hemispheric free-trade, open-borders zone.

They also show the campaign's at-times cosy relationship with mainstream journalists and television pundits - including evidence that former Democratic campaign operative (and current party head) Donna Brazile may have given the Clinton team a sneak peek at a question from a televised town hall forum during the Democratic primary.

It turns out presidential campaigns, like sausage, aren't things anyone wants to watch being made.

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Trump v the world

Let's face it, email controversies aside, right now it's just Donald Trump's world and we're all living in it. Unfortunately for the Republican nominee, that particular world is one with enemies around every corner, conspiring to seize what is rightfully his.

After announcing that he was free of "shackles" in a tweet on Tuesday morning, Mr Trump has proceeded to pick fights with members of his own party's leadership, condemn what he sees as a hopelessly biased media and warn of an international cabal that aims to subvert American democracy.

He regularly tells his supporters that they should carefully monitor polling places in "other communities" for signs of malfeasance. His own website currently has a sign-up for volunteer "election observers".

"This election will determine whether we are a free nation or whether we have only the illusion of democracy, but are in fact controlled by a small handful of global special interests rigging the system, and our system is rigged," Mr Trump said at a rally in Florida on Thursday.

His campaign, he said, was at war with "a global power structure that is responsible for the economic decisions that have robbed our working class, stripped our country of its wealth and put that money into the pockets of a handful of large corporations and political entities".

Mr Trump's latest remarks have some commentators saying he's moved from anti-Semitic dog whistles to a fully fledged bullhorn.

"Whatever Trump is thinking or means, the white nationalists and neo-Nazis he's activated will hear his speech with glee because he's channeling textbook anti-Semitic conspiracy theories, with all the code words and emotional tenor," writes liberal blogger Josh Marshall. "These are the kinds of conspiratorial, revanchist fantasies that spur violence and attacks on the mundane ordinariness of democracy itself."

Media playback is unsupported on your device Media caption Michelle Obama took on Donald Trump in a passionate speech.

The one-two Obama punch

This week also featured two of the Democratic Party's biggest guns unloading their most pointed fusillades.

President Barack Obama, who has seen his approval ratings soar to their highest point in nearly four years, appears to be running out of pejoratives to describe the Republican nominee. On Wednesday he said Mr Trump's comments on women would disqualify him from employment at a 7-Eleven convenience store, let alone the presidency.

Perhaps more concerning for Republicans up and down the ballot, however, was Mr Obama's decision to try to tie the party as a whole to what could be Mr Trump's sinking electoral ship.

"They don't get credit for at the very last minute when, finally, the guy they nominated and supported is caught on tape saying things that no decent person would even think, much less say, much less brag about, much less act on," Mr Obama said in Ohio on Thursday.

"You can't wait until that finally happens and then say that's too much and then think somehow you're showing any kind of leadership and deserve to be elected to the United States Senate."

Those remarks stand in sharp contrast with the tone Mr Obama took at the Democratic National Convention in July, when he said that Mr Trump didn't embody Republican or conservative values.

Meanwhile, First Lady Michelle Obama launched her own attack on Mr Trump - and, if anything, it was more personal and more deadly. She has the advantage of being able to speak to Americans not as a politician but as an ordinary citizen (who happens to live in the White House, of course). And in this case, she was speaking to the nation as an outraged woman.

"This is not something we can sweep under the rug as just another disturbing footnote in a sad election," she said of Mr Trump's surreptitiously recorded comments. "This was a powerful individual speaking freely and openly about sexually predatory behaviour."

That her speech took place shortly before Mr Trump's free-form conspiracy rant, media condemnation and blanket denial of sexual assault allegations just made the contrast more stark.

Image copyright Getty Images Image caption The White House may be slipping from Donald Trump's grasp

Radioactive fallout

Rhetoric and media furore aside, what this election really boils down to is a numbers game. Who can marshal financial and manpower resources and who can't? Who's got the votes in key states, and who doesn't? Messaging and momentum matter, but in the end it's only important insofar as it puts ballots in the box and numbers on the board on election day.

According to current polling, it's been a miserable week for Donald Trump. His numbers are tanking nationally, as Hillary Clinton has stretched her lead from a virtual dead heat before the first debate to high single digits.

The story in swing states is equally troubling for the Republican. He still leads in Iowa, but the pivotal battlegrounds of Ohio, Florida and North Carolina are trending away from him. Then there are states that are normally safe for Republicans - Arizona, Georgia, Utah, Alaska and Indiana - that are showing signs of tightening.

A recent poll of Texas, which Republicans have carried in every presidential election since 1976 and hasn't elected a Democrat to state-wide office since 1994, shows Mr Trump only ahead by four points.

With less than a month until election day, time is running out for Mr Trump. Next week's presidential debate could be the last opportunity he has to shake up the race - but if the past two face-offs are any indication, they are more likely to cement Mrs Clinton's lead.

Pundits and prognosticators have been wrong about Mr Trump many times in the past. His primary campaign proved to be one long refutation of conventional wisdom. After this at-times-stomach-turning week, however, it's looking more and more like it would take an unprecedented reversal of fortune for the New York businessman to add the White House to his real estate empire.