The big dig has begun.

At a time when most presidential campaigns are trying to widen their reach to the largest possible audience during the final weeks of the campaign, Donald Trump seems to be consciously contracting and burrowing down. Rattled by the release of audio tapes that revealed the predatory language he uses about women and how he plots his assaults on them, Trump’s been withdrawing into the fringe media.

This retreat is even deeper into the confines of non-reality than Trump’s previous withdrawal into the Fox News bubble. That was when, beginning late summer, Trump began appearing almost exclusively on Fox News, and then within Fox News, appearing almost exclusively on the show of his most ardent supporter, Sean Hannity, and the friendly confines of Fox & Friends.

Trump’s current withdrawal is like having Hannity then hand Trump the keys to a small bunker beneath the Fox News bubble — and trying to run a White House campaign from there.

For Trump, the Fox News bubble is a reassuring place where his campaign is always soaring and nobody cares about his tax returns. But the bunker atmosphere is perhaps even more pronounced. It’s where Hillary’s a “bitch” who needs to be imprisoned for imaginary crimes against the state (starting with Benghazi), and where talk from middle-aged men about grabbing “pussy” and trying to “fuck” married women can be dismissed as boys being boys.

It represents the darkest regions of the conservative media — it’s basically the Breitbart News dungeon. Breitbart, of course, being “a haven for people who think Fox News is too polite and restrained.”

Populated by a cranky collection of media outcasts, trolls, and bottom feeders,Trump has embraced them all, inviting them into his sanctum. As his campaign implodes, his crew is now trashing what’s left of the Republican Party, while Trump and his cadre have their eyes fixed on the prize: Obsessing over allegations of sexual assault and harassment by former President Bill Clinton.

The AM talk radio bunker is the kind of place where ‘Let Trump Be Trump’ reigns as a guiding philosophy. And at the debate, prowling the stage with a permanent scowl on his face, Trump waved that flag and marked the occasion with relentless attacks against Hillary Clinton’s husband. (Trump and his cadre of advisers even dreamt up a scheme where Bill Clinton would be forced to shake hands with his accusers.)

Why, millions of tuned-in voters likely asked, was the Republican nominee in 2016 fixating on allegations about Bill Clinton from decades ago? Especially when he’s not even running for office?

Politically, the strategy makes no sense for a general election candidate trying to lure independent voters during the home stretch of a campaign. “Veteran Republicans have long recoiled from dredging up accusations that have been leveled against Bill Clinton, considering it as a losing strategy that turns off voters,” CNN reported this week. And a YouGov survey from August confirmed that well-known fact: 62 percent of respondents said that it would be “inappropriate” for Donald Trump to “bring up Bill Clinton’s past personal behavior as a way to attack Hillary Clinton.”

The focus now from Trump and his media surrogates like Rudy Giuliani, who actually spent time in the post-debate spin room Sunday night talking excitedly about Bill Clinton’s “semen,” is that Hillary’s husband acted horribly.

Just as birtherism for years whipped up white-hot elements of the conservative base while simultaneously doing damage to the Republican Party’s image, broken-record attacks on Hillary over allegations about her husband’s behavior from two decades ago remain a political loser for Republicans.

So the obvious question is, why? Why does there remain a small, but obviously powerful pocket within the Republican Party, or at least within the Trump campaign and within the fringe confines of the conservative media, that sees this topic as the Most Important Issue Facing America.

“Right-wing journalists and operatives have been laying the groundwork for an attack on Bill Clinton’s sexual history for months,” wrote Michelle Goldberg at Slate late last year.

In truth, the plotting has been going on for years, with Sunday night’s debate being the culmination of a manic campaign to try to humiliate the first female presidential nominee in the U.S. by shaming her with allegations about her husband.

And that’s what Trump’s pre-debate stunt was all about, the “press conference” where reporters weren’t allowed to ask any questions to the Clinton accusers the candidate flew in for the event. “With Trump flanked at a long, narrow table by the Clinton accusers, it looked like a twisted version of ‘The Last Supper,’” wrote Margaret Sullivan at The Washington Post.

At Breitbart, readers were told Trump “crushed” Clinton in the debate, despite the fact that he lost the debate according to polls of viewers. Meanwhile, Trump surrogate Newt Gingrich cheered the idea that Clinton “was totally rattled by” the Trump campaign stunt.

And that appears to be the entire goal of this last-ditch campaign effort: to stoke the fascination of the bunker dwellers and their remaining hardcore supporters. “[I]t will satisfy the Breitbart wing of the conservative movement, who only ever wanted to see someone really stick it to Hillary Clinton the way they would if given the chance,” wrote Noah Rothman at the conservative magazine Commentary. “But there is no evidence that Trump will benefit from this in the polls.” (A new NBC/WSJ poll showed Trump trailing by 11 points.)

Politically, the topic represents a guaranteed dead end for the Republican Party. (Ask Newt Gingrich about the 1998 midterms.) But from Trump’s fringe media bunker, it remains an oddly irresistible target as his campaign burrows even further underground.

IMAGE: Republican U.S. presidential nominee Donald Trump speaks at a campaign rally in Ambridge, Pennsylvania, October 10, 2016.   REUTERS/Mike Segar