(CNN) As of Friday, it is not exactly clear what led to a mysterious whistleblower complaint filed against President Donald Trump that has taken Washington by storm, but it is clear that the US President wants to use Ukraine against former Vice President Joe Biden.

As with so much in the Trump presidency, it all starts with Hillary Clinton. Here's what we know:

Giuliani's accusation

Rudy Giuliani, the President's attorney and political attack dog, said on CNN Thursday night that his ongoing efforts to pursue Clinton took him to Ukraine . First he alleged, without evidence, that she and Democrats were behind the effort to discredit Paul Manafort, who is currently in prison for, among other things, laundering money he was paid as a political consultant in Ukraine. Then things turned away from Clinton.

"In the course of investigating that, I found out this incredible story about Joe Biden, that he bribed the President of the Ukraine in order to fire a prosecutor who was investigating his son," said Giuliani, alleging a media coverup. "That is an astounding scandal of major proportions, which all of you have covered up for five or six months."

From there the interview with CNN's Chris Cuomo went completely off the rails and Giuliani eventually admitted he had asked the current Ukrainian government to look into Biden.

"Of course I did!" he said.

But the President's attorney trying to get action from Ukraine is one thing. It would be something different entirely if the administration used official leverage to get a foreign country to investigate a US political rival, especially just months after special counsel Robert Mueller detailed multiple interactions between Trump's 2016 campaign and Russia but found nothing rising to the level of coordination between campaign associates and officials and Russian governmental officials.

Trump spoke with Ukraine's President Volodymyr Zelensky on July 25 and that phone call may be part of what led to the complaint against Trump.

Asked Friday about that July 25 call and whether he mentioned Biden to the Ukrainian President, Trump tried to deflect back to Biden . "It doesn't matter what I discuss," he said. "But I will say this: Somebody ought to look into Joe Biden's statement, because it was disgraceful, where he talked about billions of dollars that he's not giving to a certain country unless a certain prosecutor is taken off the case." On Friday afternoon, the Wall Street Journal reported that on that phone call Trump pressured the new president "about eight times" to work with Giuliani on Biden, citing people familiar with the matter.

Vice President Mike Pence recently met with Zelensky and was asked about Giuliani's efforts and whether the administration has held up aid to Ukraine as a result.

REPORTER: Specifically, number one, did you discuss Joe Biden at all during that meeting yesterday with the Ukrainian President? And number two, can you assure Ukraine that the hold-up of that money has absolutely nothing to do with efforts, including by Rudy Giuliani, to try to dig up dirt on the Biden family?

VICE PRESIDENT PENCE: Well, on the first question, the answer is no. But we — with President Zelensky yesterday, we discussed — we discussed America's support for Ukraine and the upcoming decision the President will make on the latest tranche of financial support in great detail.

Ukraine uses the aid in its efforts against Russian separatists, part of a long-term conflict with Russia.

Biden's efforts in Ukraine

Despite Giuliani's allegation, there has been no media coverup of the allegations against Biden. The New York Times wrote about Biden's son and his activities back in May and made clear that Trump's allies were pushing it. The President tweeted about it at the time. Since then, Trump, Giuliani and others have come back to the story repeatedly.

Asked about Trump's statement Friday, Biden said "Not one single credible outlet has given any credibility to his assertion."

"Not one single one, and so I have no comment except the President should start to be (the) President," Biden said.

I sure wish Sen Richard Burr was as interested in Biden's cushy deals w/ Ukraine & China while VP than he is in the harassment of @DonaldJTrumpJr over a CLOSED witch hunt. #Enough — Gov. Mike Huckabee (@GovMikeHuckabee) May 9, 2019

The crux of Giuliani's allegation is that Joe Biden tried to have Ukraine's top prosecutor ousted in 2016 because of an investigation into Burisma Holdings, a Ukrainian natural gas company. At the time, Hunter Biden was serving on Burisma's board.

But the reality is much more nuanced.

It is absolutely true that at the same time Burisma was being investigated, western governments, including the Obama administration wanted the prosecutor removed due to concerns about corruption in his own office. Biden too opposed the prosecutor in Ukraine, Viktor Shokin, and threatened to withhold $1 billion in loan guarantees from Ukraine. He's actually bragged about it. Recounting a trip he made to Kiev in 2016, he said it showed the US was able to get Ukraine to take corruption more seriously.

"I looked at them and said: I'm leaving in six hours," Biden said during an event at the Council of Foreign Relations in 2018 . "If the prosecutor is not fired, you're not getting the money. Well, son of a bitch. He got fired. And they put in place someone who was solid at the time."

None of this is a particularly good look for the Bidens, but there's no proof or suggestion of any actual wrongdoing.

At least one former official in the prosecutor's office said the investigation into Burisma had already been shelved by the time Joe Biden was threatening to withhold financial aid unless Ukraine replaced its top prosecutor. It's also not clear if Hunter Biden was a focus of that investigation when it was occurring.

In an interview on May 14 posted on Facebook by his assistant, Ukrainian Prosecutor General Yury Lutsenko said Burisma paid an entity connected to Hunter Biden "millions," but added, "from my point of view, a board member can be paid whatever a company decides ... they didn't violate any Ukrainian laws."

He said that he said it was a matter for US law to consider, not Ukrainian investigators.

Lutsenko in May said he was looking to "reanimate" an investigation of Burisma, Hunter Biden's former employer -- but that apparently never happened. Lutsenko left office in August after the new administration of Zelensky took office.

Giuliani himself went to meet with a representative of Zelensky after the President's call with Trump in July.

According to Democratic Sen. Chris Murphy of Connecticut, Ukrainian officials understand there is a link between what Giuliani was asking of the Ukrainians to do and getting US military aid.

Murphy met with the Ukrainian President a few weeks ago and described the scene on Twitter.

"Zelensky did not explicitly connect the two in our meeting, but he was VERY concerned about the cut off of aid, and VERY aware of the conversations that Rudy Giuliani was having with his team. I told him it was best to ignore requests from Trump's campaign operatives. He agreed," Murphy explained in a series of tweets.

Zelensky did not explicitly connect the two in our meeting, but he was VERY concerned about the cut off of aid, and VERY aware of the conversations that Rudy Giuliani was having with his team. I told him it was best to ignore requests from Trump's campaign operatives. He agreed. — Chris Murphy (@ChrisMurphyCT) September 20, 2019

I don't know what is in the whistleblower complaint, but it was clear to me that Ukraine officials were worried about the consequences of ignoring Giuliani's demands. And of course they were. That's why presidents shouldn't have their campaigns talking to foreign leaders. — Chris Murphy (@ChrisMurphyCT) September 20, 2019

Trump's playbook

Fostering conspiracy theories about his rival was a strategy that worked for Trump in 2016 as he used decades of conservative conspiracy theories about Hillary Clinton to label her "crooked" and suggest she should be in jail rather than the White House.

Biden, however, is not followed by the same political taint as the Clintons and the effort by Trump and his allies may now have led to a whistleblower sounding the alarm under a law meant to protect intelligence officials for uncovering improper activity.

The specifics of the whistleblower complaint remain a mystery and could remain that way as Trump's new acting Director of National Intelligence refuses to share information about the complaint with Congress. The Intelligence Community Inspector General has caused alarm by publicly saying he is being kept from doing his job.

Father and son

Hunter Biden's personal life and substance abuse issues have already caused angst for the former vice president.

The overlap between the father and son's political and business interests have fueled GOP attacks that Biden is little more than a self-interested politician. Whether the facts fully support that case appears to be an afterthought for his critics.

GOP researchers have been digging through Hunter Biden's career history as well as the points where it appears to intersect with his father's, particularly where it pertains to Ukraine and China, another topic Giuliani brought up during his interview with Cuomo.