Democratic nominee Hillary Clinton and GOP nominee Donald Trump have hammered each other for the last year over allegations of corruption.

The press has found innumerable instances of shady dealings on the part of Trump and his businesses, while Clinton has been investigated for possible financial schemes – along with a number of other debunked scandals. And that doesn't even touch the decades of financials scandals attached to both of them, some rightly, and some completely wrong.

But no matter which one is elected, he or she likely won't come close to being the most corrupt president in American history. President Barack Obama has also been derided as such by pundits on both sides of the aisle, but whatever chicanery his administration committed is far outweighed by that of past presidents, whose terms in office were steeped in greed, graft, bribery, and theft.

Who were the most corrupt administrations in American history?

Some of the answers won't surprise you at all, while others are pretty shocking.

Ronald Reagan

Reagan's administration was beset by an endless string of scandals.

• A huge procurement scandal called Operation Ill Wind, which gutted the military and Defense Department.
• A massive scandal that involved HUD.
• A copyright infringement case in the Department of Justice called the Inslaw Affair.
• The EPA's Sewergate scandal.

By far, the biggest scandal that tarred Reagan was Iran-Contra, a complex scheme between 1985 and 1986 under which the heads of the CIA and National Defense Council hatched a conspiracy to sell missiles to Iran in exchange for the return of U.S. hostages.

The Iranian money would then fund Contra rebels trying to overthrow the left-wing government of Nicaragua.

The scheme violated both the embargo against Iran and an amendment prohibiting more money going to the Contras.

After the deal came to light, Reagan went on national TV in late 1986 and claimed arms weren't being traded for hostages – then had to go on TV again months later to admit the trades did happen.

Sixteen people were indicted afterward, including Reagan's former secretary of state and numerous CIA and military officials.

Richard Nixon

The gold standard of presidential corruption, Nixon is the only POTUS in history to have to resign as he was facing certain impeachment after the Watergate scandal.

But Watergate isn't the only scandal that tarred Nixon and his administration.

• Nixon's vice president, Spiro Agnew, also had to resign about a year before Nixon did after he was implicated in a tax evasion scheme.
• Nixon's CIA director, meanwhile, was convicted of conducting illegal surveillance on U.S. journalists and plotting assassinations in Chile.
• Nixon's SEC chair had to resign after less than three months in office after altering a negative finding against a Nixon fundraiser.

Warren G. Harding

Harding served only two years before his death in 1923, but his administration was consumed by both personal and political scandal.

• Harding was a notorious philanderer, and in the waning days of his time in the senate, he was blackmailed by a former mistress who threatened to expose their affair if Harding didn't vote against war with Germany.
• Harding's cabinet had the dubious distinction of being the first to have a member convicted of a crime, after Secretary of the Interior Albert Fell was sent to prison as part of the Teapot Dome scandal, in which Fell accepted bribes to lease the Navy's oil reserves at Teapot Dome, Wyoming, to private companies.
• The Teapot Dome scandal also claimed Harding's secretary of the Navy.
• Harding's attorney general resigned in 1924 over a bootlegging kickback scheme.
• Two other Harding department heads were convicted of bribery and fraud: Charles Forbes, for massively defrauding the government while building VA hospitals, and Office of Alien Property head Thomas Miller, for illegally selling German patents seized after World War I.

Ulysses S. Grant

Grant himself was known for his honesty, but his administration was likely the most corrupt in the 19th century.

A near-ceaseless flow of money from speculation and western expansion led to an epidemic of corruption, and Grant responded by stubbornly protecting those accused of graft.

• A massive conspiracy to pilfer tax revenue from whiskey sales, called the Whiskey Ring, snared more than 100 federal, state, and local officials.
• The secretaries of the Navy, of war and of the treasury all faced allegations of bribery and taking kickbacks.
• The Salary Grab Act was passed by Congress at the end of Grant's first term to enact gigantic retroactive pay raises for itself and to increase the salary of the president.
• Grant's administration was gutted by the Credit Mobilier scandal, in which a construction company massively overcharged the Union Pacific Railroad. The company pulled off the scam thanks to millions in bribes paid to the vice president, the secretary of the treasury, four senators, and the speaker of the House.

Andrew Jackson

The inherently corrupt "spoils system," under which government officials were hired based on what they'd done for the incoming administration rather than on merit, dominated politics in the 19th century. It began with Andrew Jackson, who purged the ineffectual career bureaucracy of past administrations — and his administration was beset by a mob of office-seekers in response.

Jackson was unable to keep federal offices nonpartisan and rewarded lucrative jobs to donors, friends, business associates, newspaper editors who had written in support of Jackson, Army veterans, and seemingly random characters.

The result was a cavalcade of theft and corruption in distant offices and military posts, including $1.2 million embezzled from the New York City Customs House, the most lucrative point of entry in the U.S.

It took decades to dismantle the spoils system that started under Jackson — and it can be argued that it's never gone away completely.