From his eyebrow-raising dealings in Delaware, China and Ukraine to controversies involving drug use and child support, Hunter Biden is no stranger to scandal. The son of former vice president and Democratic presidential candidate Joe Biden has faced accusations of corrupt behavior from both sides of the political aisle, and played a starring role in the recently concluded impeachment proceedings against President Trump.

The younger Biden's distinct scandals are best understood in rough chronological order because Republicans have argued that Biden's apparently irresponsible behavior only made it more likely that his later sweetheart gigs were obtained not through merit, but because of connections that he could monetize.

Delaware

In 2008, both The New York Times and The American Spectator highlighted Hunter Biden's sweetheart gigs while his father rose in political prominence. The articles, written as Barack Obama and John McCain vied for the White House, found that Hunter Biden received consulting fees from the financial services company MBNA from 2001 to 2005 — while his father, then a senator, was pushing successfully for legislation that would make it harder for consumers to file for bankruptcy protection.

The precise amount of the payments was unclear, but a company official once said Hunter Biden was receiving at least a $100,000 per year retainer, the Times reported. Hunter Biden, now 49, previously had been an executive at MBNA beginning in 1996, but the consulting fees came years after his departure from the company as a full-time employee.

Aides to then-presidential candidate Barack Obama at the time denied that any lobbying had occurred, and insisted the payments were proper. However, that explanation was immediately treated with skepticism. The Trump campaign recently posted a contemporaneous interview in which an incredulous Tom Brokaw asked Joe Biden whether it was "inappropriate" for the then-senator to have his son "collecting money from this big credit card company while you were on the [Senate] floor protecting its interests."

Hunter Biden's previous work as an executive at MBNA from 1996 to 1998 also has raised what critics called red flags.

Rachel Mullen, a former senior personal banking officer at MBNA from 1994-2001 who later went into Republican politics, tweeted that managers referred to the younger Biden as "Senator MBNA" after he was hired into a lucrative management-prep track right after he graduated from Yale Law School.

An MBNA source who previously worked at the company told Fox News that other employees heard Hunter Biden boasting that his salary was unusually high, even for the management-prep track — which was widely seen in the company as a way to groom and pamper well-connected executive candidates with powerful family members.

The source said Biden's "Senator MBNA" nickname was not politically motivated, but rather reflected a widely held belief among managers – who did not work directly with Biden – that he essentially was engaged in lobbying.

The Bidens' connections with MBNA apparently ran deep. In a January 2008 article entitled "The Senator from MBNA," columnist Byron York recounted how then-MBNA vice chairman John Cochran paid "top dollar" for Joe Biden's home in February 1996, just prior to his Senate reelection bid, and that "MBNA gave Cochran a lot of money – $330,000– to help with 'expenses' related to the move."

The $1.2M sale was a "pretty darned good deal for Biden," York wrote, noting that "Cochran simply paid Biden’s full asking price" even though the "house needed quite a bit of work; contractors and their trucks descended on the house for months after the purchase."

Asked how Cochran and Biden found each other for the sale, an MBNA spokesperson told York: "That’s a very personal question."

Aside from MBNA during this period, the younger Biden worked at a lobbying firm and served on the board of Amtrak -- a prestigious role he apparently obtained through his connections, although Democrats claimed he deserved the post because he traveled regularly on trains.

"Hunter Biden has spent a lot of time on Amtrak trains. Like his father, like our congressman, Mike Castle, and myself, Hunter Biden has lived in Delaware while using Amtrak to commute to his job as we commute to our job in Washington almost every day of the week," Democratic Delaware Sen. Tom Carper said at a hearing on Biden's nomination to the Amtrak board in June 2006. "You know, you learn a lot about what could work and what would work better at Amtrak by riding trains and talking to the passengers, the commuters, the passengers, the folks who work on the trains and make them work every day."

Navy expulsion

In 2014, Hunter was kicked out of the military after testing positive for cocaine. The Navy said that Biden, a former lobbyist who worked at a private equity firm, was discharged barely a year after he was selected for his part-time position as a public affairs officer in the Navy Reserve.

Two people familiar with the situation quickly told the media that Biden was discharged because he failed a drug test in 2013. The Wall Street Journal first reported Biden’s discharge and failed drug test.

TREASURY COMPLIES WITH HUNTER BIDEN INQUIRY, HANDS OVER SENSITIVE DOCS

An attorney by training, Biden applied to join the Navy Reserve as a public affairs officer and was selected in 2012 — one of seven candidates recommended for a direct commission for public affairs. A board of senior Navy officers interviewed Biden before making the recommendation.

Because he was 42 at the time, he needed a special waiver to be accepted. Cmdr. Ryan Perry, a spokesman for the Navy, said Biden had been assigned to the Navy Public Affairs Support Element East, based in Norfolk, Va.

Ukraine

Hunter Biden and and his friend Devon Archer joined the natural gas company Burisma Holdings board in April 2014. Biden apparently cannot speak Ukrainian and had no relevant natural gas experience.

Joe Biden has acknowledged on camera that in spring 2016, when he was vice president and spearheading the Obama administration's Ukraine policy, he successfully pressured Ukraine to fire top prosecutor Viktor Shokin. At the time, Shokin was investigating the notoriously corrupt Burisma Holdings — where Hunter's role was especially lucrative. The vice president threatened to withhold $1 billion in critical U.S. aid if Shokin was not fired.

"Well, son of a b---h, he got fired," Biden joked at a panel two years after leaving office. Shokin himself had already been widely accused of corruption.

WHOOPS: BIDEN CAMPAIGN TOUTS UKRAINE ACTIVIST WHO CALLED HUNTER'S ACTIONS 'VERY BAD'

Critics alleged Hunter Biden might have been selling access to his father, who had pushed Ukraine to increase its natural gas production.

Government officials have raised similar concerns. During the House impeachment proceedings, a career State Department employee testified that he had flagged Hunter Biden's apparent conflict of interest, but was told essentially not to bother the vice president's office.

"Impossible to justify $50k/month for Hunter Biden serving on a Ukrainian energy board w zero expertise unless he promised to sell access," political scientist Ian Bremmer previously tweeted.

Joe Biden has said he never discussed his son's overseas business dealings -- an assertion seemingly contradicted by both his son and a photo exclusively obtained by Fox News.

“I know I did nothing wrong at all. Was it poor judgment to be in the middle of something that is a swamp in many ways? Yeah," Hunter Biden said in an exclusive sit-down with ABC's Amy Robach at his Los Angeles home last October.

TENSIONS FLARE IN CONGRESS, AS GOP REP BRINGS UP HUNTER BIDEN'S COCAINE USE

He acknowledged he may not have gotten the job were it not for his connections to the vice presidency.

In the ABC News report last year which also delved into the Bidens' China dealings, journalist Tom Llamas called it "strange" that Ukrainian natural gas company Burisma Holdings, widely accused of corruption, had appointed Hunter Biden to its board of directors -- and agreed to pay Hunter Biden's company "more than a million dollars a year."

"Hunter -- a lawyer, who had just been discharged from the Navy Reserves for testing positive for cocaine," Llamas says incredulously. "He had served on other boards, but had no known experience in Ukraine or natural gas."

Earlier this month, the Treasury Department complied with a Senate inquiry into the younger Biden's business dealings in Ukraine and reportedly handed over highly sensitive financial records and "evidence of questionable origin."

China

Top Republican senators recently requested travel records from the Secret Service that might shed light on Hunter Biden's dealings in China, which Trump has long said merit a state investigation.

Much of the focus concerns Biden's position as one of nine directors at BHR -- a private-equity company controlled by Chinese government-backed stakeholders. Senate Finance Committee Chairman Chuck Grassley, R-Iowa, and Senate Homeland Security and Governmental Affairs Committee Chairman Ron Johnson, R-Wis., said the arrangement raised red flags.

"In December of 2013, one month after Rosemont Seneca's joint venture with Bohai Capital to form BHR, Hunter Biden reportedly flew aboard Air Force Two with then-Vice President Biden to China," the senators wrote. "While in China, he helped arrange for Jonathan Li, CEO of Bohai Capital, to 'shake hands' with Vice President Biden."

"Afterward," they continued, "Hunter Biden met with Li for reportedly a 'social meeting.' After the China trip, BHR's business license was approved.

Then, in 2015, BHR joined with Aviation Industry Corporation of China (AVIC) to acquire Henniges, which was the 'biggest Chinese investment into U.S. automotive manufacturing assets to date.'"

The senators also sought travel records relating to Biden's trips to Ukraine, if any.

Last year, Biden stepped down from the board of BHR and said he wouldn't take similar roles if his father won the presidency. The Wall Street Journal reported that BHR Partners filings show that while Hunter was a director of BHR since its founding, he didn't become a shareholder until October 2017.

Trump has specifically accused Biden of walking "out of China with $1.5 billion in a fund.” The Journal reported in 2014 that BHR was trying to raise that much money to invest outside of China, but it's otherwise unclear what the president was referencing.

Kids

In January of this year Hunter Biden agreed to pay monthly child support retroactive to November 2018, temporarily ending a standoff that began after the judge in his Arkansas paternity case ordered him to appear in person for a hearing to explain why he shouldn't be held in contempt.

But, the standoff reignited in March, when Biden apparently failed to meet a court deadline to turn over additional financial documents. Republicans suggested he was hiding evidence of corruption. The matter remains pending.

Biden had previously denied paternity, before a DNA test proved otherwise.

HUNTER BIDEN FINALLY AGREES TO PAY CHILD SUPPORT FOR KID FATHERED WITH EX-STRIPPER

The court redacted the amount of child support that Biden agreed to pay, pursuant to his agreement with plaintiff Lunden Alexis Roberts, who alleged Biden was an entirely absent father.

However, Independence County Circuit Court Judge Holly Meyer noted that she "lacks sufficient information" to determine the appropriate amount of "permanent" child support "based off the defendant's income," and that modifications to the child support owed each month could be made based on additional evidence.

Contempt proceedings over Biden's repeated failure to turn over relevant financial documents were only delayed until March 1, and Biden apparently has not resolved the issue.

"After months of hiding, one has to wonder if the reason Hunter Biden continues to defy the court is because there are financial documents could shed light on his father’s massive conflicts of interest as vice president," Republican National Committee (RNC) spokesman Steve Guest told Fox News.

READ THE ORDER REQUIRING BIDEN TO PAY CHILD SUPPORT

The paternity dispute has presented headaches for the elder Biden ever since a court filing showed that DNA results indicated he was now a grandfather. Joe Biden tangled with a Fox News reporter on camera when asked about that development last November.

"No one has said my son has done anything wrong." — Joe Biden

"I'm wondering if you have a comment on this report, and court filing, out of Arkansas, that your son Hunter just made you a grandfather again," Fox News’ Peter Doocy asked.

"No, that’s a private matter and I have no comment," Biden fired back before attacking the reporter.

"Only you would ask that," Biden said. "You're a good man. You're a good man. Classy."

Campaigning late last year, Biden has also lashed out at voters -- even appearing to call one man "fat" for bringing up issues with his son's possible corruption and questioning his fitness for office.

“You’re a damn liar, man," Biden said. “Let’s do push-ups together here, man. Let’s run. Let’s do whatever you want to do. Let’s take an IQ test. ... No one has said my son has done anything wrong."

The Associated Press contributed to this report.