There's a conspiracy theory that Donald Trump is a double agent on a "false flag" mission to ensure Hillary Clinton becomes the next president of the United States. 

It's wacky, but there's logic to it.

The idea is that Trump will deliberately do so much damage to the Republican brand that voters will turn away from it with a shudder and usher the Democrat Clinton into the White House. 

Trump's rival for the Republican presidential nomination, Jeb Bush, speculated about something similar on Twitter in December.

"Maybe Donald negotiated a deal with his buddy @HillaryClinton," Bush tweeted shortly after Trump again raised the prospect of an independent campaign for president if Republicans aren't nice to him.

An independent challenge would split the anti-Clinton vote and probably give her a cakewalk to the presidency in November.

But it's the evidence accumulated over many years that Clinton and her husband, the former president, have a close private relationship with Trump that has kept the conspiracy theory alive.  

It surfaced in July when Trump first began to surge in public opinion polls.

At that time, the Washington Post reported that Bill Clinton had called Trump before he entered the race and the two talked politics.

Warm on the outside

Clinton's office confirmed the call but said the former president offered neither advice nor encouragement about Trump's candidacy.

Donald Trump

Donald Trump reportedly received a call from Bill Clinton before he entered the race for the Republican nomination and the two talked politics. (Ralph Freso/Getty Images)

Trump's people suggest there was more to it than that.

In any case, stories were soon rolling out recalling the long and outwardly warm relationship between the Clintons and Trump.

Photos of Trump's most recent wedding (No. 3, in ­2005) at his Palm Beach, Fla., compound show the smiling Clintons posing together with Donald on one side of them and his new bride, Melania, on the other, like the happiest-looking bookends you've ever seen. 

More photos show the former president with Trump on his golf courses.

"I like him and I love playing golf with him," Clinton has said.

Really nice things

To suggest less innocent connections, hard-core conspiracy theorists such as "The Daily Sheeple" point to Bill Clinton's elevation of a Trump sister, Judge Maryanne Trump Barry, to a U.S. Court of Appeals in 1999.

Plus, Trump has said some really nice things about Hillary Clinton over the years.

When she was secretary of state, for example, Trump told Fox News that she "is a terrific woman" who "really works hard" and "does a good job."

Years before that, on CNN, he said: "Hillary's a great friend of mine. Her husband's a great friend of mine. They're fantastic people."

And when he's with fantastic people, Trump can hardly be expected not to hand out some cash. 

Trump has donated thousands of dollars to many politicians — Democrats and Republicans — and some of that money has gone to Hillary Clinton's earlier campaigns for the Senate and the presidency.

DEM 2016 Bill Clinton

Donald Trump has donated to Hillary Clinton's earlier campaigns for the Senate and the presidency and given at least $100,000 to the Clinton Foundation, which was founded by Bill Clinton. (Charlie Neibergall/Associated Press)

He's also given at least $100,000 to The Clinton Foundation, according to the non-profit.

The donations might be evidence that Trump is in cahoots with the Clintons to shape the 2016 race were it not for the fact it was all only business.

No filter

Just ask him.

The good, the bad and the ugly of Trump is that he has no filter. He says what suits him whenever it suits him.

On the subject of politicians and money: "When they call, I give. And you know what? When I need something from them two years later, three years later, I call them. They are there for me."

And so it was with the Clintons, he said.

Trump shone this bright light into the dark corners of power during the first Republican debate in August.

While he was at it, he also thought to clear up any misunderstanding about why the Clintons came to his wedding 10 years ago.

" 'Hillary Clinton,' I said, 'Be at my wedding' and she came to my wedding," said Trump. "She had no choice because I gave to a foundation."

The conspiracy theorists will be the last to accept Trump for what he is: not a Clinton operative but someone who's often been called a narcissist who's dead serious about becoming president. 

Not losing sleep

If old acquaintances, even a former president and his first lady, get roughed up along the way, that's not something he's going to lose sleep over. 

When Hillary Clinton recently said he had "a penchant for sexism," Trump didn't hesitate to fire back that her husband is "one of the great abusers of the world."

There will be more of this in the weird battle over who has the worst record with women: him for the things he says about women or her for sticking up for her husband.

The odds that Trump will win the nomination are slimmer than they look in national opinion polls. For one thing, his strongest support is among self-identified Republicans who last registered as Democrats and are least likely to vote, according to new research by Civis Analytics.

Still, it's delicious to speculate about the possibility that Hillary Clinton and Donald Trump will face each other across the stage in presidential debates this fall.

Hillary Clinton, the first woman to top the ticket of a national political party, and Donald Trump, the man Fox News anchor Megyn Kelly reminded us has called women "fat pigs, dogs, slobs and disgusting animals," together again after all their history.