How did Ken Starr's investigation into President Clinton resemble — and differ from — the ongoing Mueller investigation? Here's everything you need to know:

Why was Clinton investigated?

It began over the Whitewater scandal, a long-running controversy concerning a failed 1978 land deal in Arkansas. The Clintons' business partner in that project defrauded a small savings association and an investment firm, and some of the parties involved charged that the president and his wife had benefited from the fraud. In January 1994, Attorney General Janet Reno appointed Robert Fiske as a special prosecutor to investigate the Clintons' involvement. Seven months later, however, a Republican-leaning panel of judges dismissed Fiske — on the basis that his appointment by Clinton's attorney general represented a conflict of interest — and appointed Ken Starr as an independent counsel, reporting to Congress, not to the Justice Department. Starr, who had served as solicitor general under President George H.W. Bush, was a staunch Republican. Clinton loyalists immediately cried foul, denouncing the probe as "tainted" and a partisan "witch hunt." "This will last as long as [Clinton is] president and beyond," warned White House Counsel Bernard Nussbaum. "They'll be investigating things years from now that we haven't even dreamed about today."

Were those fears realized?

Yes. While Starr ultimately found no criminal wrongdoing by the Clintons regarding Whitewater, he broadened his investigation to include many other controversies swirling around the White House. In January 1998, a civil servant named Linda Tripp told Starr's team she had recordings of Monica Lewinsky, a former White House intern, discussing an 18-month affair she'd had with the president. With Reno's approval, Starr expanded his investigation to include Lewinsky. The president fiercely denied the affair with Lewinsky — first in a sworn affidavit while testifying in a case involving Paula Jones, an Arkansas state employee who had accused Clinton of sexual harassment, and then to reporters and the public, saying, "I did not have sex with that woman."

What did Starr do?

He built a comprehensive case that Clinton was lying by compelling White House staff and Secret Service members to testify. After six months of negotiations to get Clinton to testify, Starr subpoenaed the president, and Clinton agreed to testify "voluntarily" for a grand jury, with his lawyers present. That precedent now hangs over the negotiations taking place between Mueller and Trump's legal team over whether the current president will testify in the Russia investigation. "No matter how much huffing and puffing Trump's lawyers do," says Lanny Davis, Clinton's former special counsel, "they cannot escape a grand jury–issued subpoena."

What happened in the interview?

Clinton admitted that he'd had "inappropriate intimate contact" with Lewinsky. But he insisted he hadn't perjured himself during the Jones case — arguing that he understood "sexual relations" to mean sexual intercourse, not oral sex — and denied instructing Lewinsky and others to lie to investigators. Starr submitted his report to Congress three weeks later, and lawmakers voted to make it public. The 445-page document specified 11 possible grounds for impeachment, mostly related to the coverup. In December, the GOP-controlled House of Representatives voted almost entirely along party lines to impeach Clinton for perjury, 228-206, and obstruction of justice, 221-212. (Two other charges were voted down.) But after a five-week trial in the Senate, Clinton was acquitted on both charges. All 45 Democratic senators voted "not guilty" on the obstruction charge, along with five Republicans, and the 50 "guilty" votes fell far short of the 67 required to oust Clinton from office. On the perjury charge, 55 senators voted "not guilty."

How does Mueller's probe compare?

Unlike Starr, who gave interviews, Mueller has adopted a very low profile, and there have been few, if any, leaks from his team. But their tactics are similar: Starr persuaded Lewinsky and other witnesses to cooperate by threatening them with long jail terms for lying, just as Mueller has done. Also familiar are the aggressive attempts by Trump's backers to discredit Mueller. During the Starr investigation, Sen. Pat Leahy (D-Vt.) claimed the independent counsel was "totally out of control" and fixated on "trying to topple the president." Clinton aides demanded an investigation into the investigation; Democratic lawmakers called on Starr to step down. "Clinton only survived," says Dick Morris, one of his former advisers, "because he made Ken Starr the enemy."

Can Trump do the same?

He will certainly try. Clinton's supporters had more basis for their complaints: Starr was a partisan Republican when he was appointed; Mueller is a lifelong Republican who was appointed FBI director by Republican George W. Bush, although several of his investigators are Democrats. Because the charges against Clinton primarily involved a private sexual affair, the public generally took a dim view of Starr's charges: Clinton's approval ratings soared to their highest-ever level during the impeachment. That dynamic — reinforced by the Democrats' strong showing in the 1998 midterms — convinced senators that removing the president from office over the Lewinsky affair would be political suicide. A similar principle applies with Mueller's investigation. If he finds grounds for impeachment, public opinion will serve as the ultimate jury, and Congress' decision about whether or not to oust Trump will be largely a political calculation.

Sex in the Oval Office

Starr's final report did not merely provide evidence that Clinton had had an affair with Lewinsky — it described their encounters in lurid, almost pornographic detail. The document quoted extensively from the former intern's testimony, with graphic descriptions of oral sex, touching and kissing, and the use of a cigar in a sex act. It described the pair's flirty relationship: Before their first kiss, Lewinsky said, she pulled up her jacket to reveal her thong; she addressed him as "Handsome," and he called her "Sweetie," "Baby," and "Dear." Famously, the report revealed that semen found on a blue dress belonging to Lewinsky matched Clinton's DNA. These salacious details shocked many Americans, and amplified criticism that Starr was a partisan moral scold trying to destroy the president. In his defense, Starr said the descriptions bolstered Lewinsky's credibility as a witness and helped build the clearest possible case that the president's original denial was false. The sexual details, he said, were "indispensable."