For Democrats, the breakup was a long time coming, a political romance with the Clintons that started with a heady, upstart 1992 campaign, was tested during Bill Clinton's impeachment, and finally ended when the couple's home state senator said the former president should have resigned over sexual misconduct allegations.

But President Donald Trump and the GOP just can't seem to quit the out-of-power Clintons. Trump tweets frequently (and accusingly) about the woman he beat out for the White House in 2016, while Capitol Hill Republicans are mounting their own Clinton investigations and demanding that the Department of Justice do the same. In October, House and Senate Republicans announced formal inquiries into two matters involving the former first couple: an Obama-era uranium deal involving Russia that accusers charge was tied to support for the Clinton Foundation, and a separate investigation of how the FBI handled then-Secretary of State Hillary Clinton's private email server.

Some congressional Republicans have gone further. Rep. Jim Jordan, R-Ohio, wants a special counsel to look into how the FBI decided not to charge Clinton for her handling of classified information while using the private email server. That's in spite of the fact that Hill Republicans, after exhaustive, campaign-season hearings and investigations of the matter, could not come up with evidence of wrong-doing by the Democratic presidential nominee.

Trump himself has demanded formal inquiries into a slew of matters related to the Clintons, ranging from the email controversy to what he calls a "fake dossier" of Trump misconduct. (The dossier was funded by both Republicans and Democrats.)

Meanwhile, Democrats have appeared to make the break, with New York Sen. Kirsten Gillibrand, a potential 2020 presidential contender, saying she thinks in retrospect that Bill Clinton should have stepped down over allegations of sexual bad behavior. Kathleen Sebelius, Obama's secretary of Health and Human Services, chimed in as well, saying her party "doubled down on not only bad behavior but abusive behavior" by targeting women who had accused Clinton.

Now, Trump and congressional Republicans have an ambitious legislative agenda, a new tax law to sell to a skittish public, and a 2018 midterm campaign season that is not looking good for GOP incumbents. So why can't they let go of Bill and Hillary Clinton – both of whom are out of office, and neither of whom is expected to run for any office, ever again?

Follow the money, says David Cohen, a political science professor at the University of Akron.

"The Clintons have always been good fundraising fodder for the Republicans. They've always hated them since their rise in Arkansas," Cohen says. "The far right has always despised the Clintons, especially Bill Clinton, and the conspiracy theorists think there's something even more untoward about the Clintons, aside from misbehavior with Bill Clinton with regards to women. It's a cash cow for them."

The Clintons have long been an irritant to Republicans, who couldn't figure out how the man they described as "a failed governor from a small state" managed to oust incumbent president George H.W. Bush in 1992 (though the elder Bush later became friends with Clinton, working with him on disaster relief). Republicans impeached Clinton in 1998, but they not only failed to get a conviction, they lost House seats despite the Monica Lewinsky matter that led to the impeachment.

The couple continued to recover politically, much like an inflatable carnival clown that bounces back up, grinning, every time it is knocked down. Hillary Clinton became a U.S. senator, then a secretary of state, then the first major party female presidential nominee. Only Trump was able to fell Clinton – and yet, he's still fighting, calling her "Crooked Hillary" and the "worst (and biggest) loser of all time" on his Twitter feed.

According to the Trump Twitter Archive, the president has tweeted about Hillary Clinton 75 times since taking office – far more than the 19 times he's mentioned veterans or the 34 times he's mentioned his own daughter, Ivanka (and that includes retweets of her tweets).

Most recently, Trump on Thursday tweeted a criticism of the magazine Vanity Fair, which recently apologized for a feature that fell flat about New Year's resolutions Clinton might make (such as taking up knitting). Said Trump, "Vanity Fair, which looks like it is on its last legs, is bending over backwards in apologizing for the minor hit they took at Crooked H. Anna Wintour, who was all set to be Amb to Court of St James's & a big fundraiser for CH, is beside herself in grief & begging for forgiveness!"

Wintour actually edits the fashion magazine Vogue – not Vanity Fair. And it was under the Obama administration that Wintour was reportedly under consideration for an ambassadorship.

Clinton herself has barely tweeted about Trump personally after congratulating him on his upset win – though she has made implicit references to presidential policy, whether it's the Children's Health Insurance Program or help for hurricane-ravaged Puerto Rico. And she has expressed bafflement at Trump's continued attention to her.

"Apparently, you know, my former opponent is obsessed with my speaking out," Clinton said at a forum in Little Rock, Arkansas to commemorate the 25th anniversary of her husband's election. "Apparently there was another, somebody told me, tweet today. Honestly, between tweeting and golfing, how does he get anything done? I don't understand it. Maybe that's the whole point."