Vladimir Putin, the president of Russia, has become such a boogeyman in American politics that public statements sounding even remotely in his favor elicit cries of treason.

President Donald Trump kicked over a huge hornet’s nest in Helsinki, Finland, on Monday when he failed to challenge Putin forcefully on interference in the 2016 presidential election and questioned whether he accepts the judgment of U.S. intelligence agencies about Russia’s role in the meddling.

Trump has complained that the obsessive focus on the election and the probe led by special counsel Robert Mueller are derailing efforts to build better relations with the world’s second-largest nuclear power.

Russia experts are deeply skeptical that Putin is disposed to constructive cooperation with the United States. But Trump seems to believe he might succeed. And he’s not the first occupant of the Oval Office to think so.

“It’s not just Trump,” said Robert Kaufman, a foreign-policy expert at Pepperdine University in California. “It’s American presidents in general.”

Trump is the fourth American president Putin has dealt with since he first took control at the Kremlin in 2000. Here is a look at how the others have fared:

Bill Clinton. The 42nd president did not have much time left in office when Putin won his first election, but Clinton tried to lay the groundwork for a good relationship amid growing disputes over expansion of the North Atlantic Treaty Organization (NATO) and concerns over the long-term health of the then-nascent Russian democracy.

During a news conference after meeting Putin in June 2000, Clinton expressed optimism.

“If you want to know what my personal assessment is, I think he is fully capable of building a prosperous, strong Russia, while preserving freedom and pluralism and the rule of law,” Clinton said.

In reality, Putin quickly moved to isolate reformers, curtail civil liberties and press freedom, allow wealthy oligarchs to exert greater influence, and crush a rebellion in the breakaway republic of Chechnya.

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George W. Bush. Clinton’s successor met Putin in June 2001 at a summit in Slovenia and came away thinking he had a partner.

“I looked the man in the eye,” Bush said in remarks that drew much scorn at the time. “I found him very straightforward and trustworthy — I was able to get a sense of his soul.”

Bush kept up the charm offensive, inviting Putin to his ranch in Texas in November of that year. The two leaders rode around the expansive property in a jeep, traded jokes and pledged to bring stability to Afghanistan. They dined on barbecue, danced to “Cotton-Eye Joe,” and visited a local high school.

But disputes over missile defense remained a point of contention. After winning a second term in 2004, with popularity high at home, Putin spoke of restoring Russia to a position of prominence on the world stage. And in perhaps the most revealing statement about how Putin views the world, he declared during a 2005 address at the Kremlin that the breakup of the Soviet Union was the “greatest geopolitical catastrophe of the 20th century.”

Russia prosecuted the country’s richest man, Mikhail Khodorkovsky, which Kremlin critics saw as retaliation for the businessman’s support of Putin’s political opponents.

By the end of the Bush presidency in 2008, Russia had invaded the nation of Georgia in support of rebels in the province of South Ossetia who wanted to rejoin the Bear. Putin at the time had given up the presidency and become prime minister, but most observers contend he remained the true power in Moscow.

Barack Obama. Despite Russian aggression, Obama came into office determined to change the U.S.-Russian relationship, launching the infamous “Russian reset” policy. His secretary of state, Hillary Clinton, presented her Russian counterpart with a red button labeled “reset” to visualize the new tone. (The administration flubbed the execution, however, using a Russian word that translated into “overload” rather than “reset.”)

In August 2009, Obama endured a lecture from Putin that lasted nearly an hour at a breakfast between the two leaders. Obama appeared unbowed by Putin’s complaints about alleged misdeeds by the United States.

Related: Not ‘Much Daylight’ Between Trump and Obama on Russia, Actually

“I don’t have a bad personal relationship with Putin … I know the press likes to focus on body language, and he’s got that kind of slouch, looking like the bored kid in the back of the classroom,” he said. “But the truth is, is that when we’re in conversations together, oftentimes it’s very productive.”

In 2010, the two countries signed the new Strategic Arms Reduction Treaty (START) in which both sides agreed to reduce strategic nuclear arms by half.

“To get there, you have to have a pretty healthy opinion about your persuasive abilities.”

As late as 2012, Obama held onto hope that Russia and the United States could be partners. In a hot mic incident, Obama could be heard telling Russian President Dmitry Medvedev that he would have more “flexibility” after he got past the next election. Medvedev dutifully replied he would “transmit” the message to Putin.

But Putin proved no more amenable to Obama in the long run than he was to previous presidents. Russia invaded Ukraine in 2014 and annexed Crimea. In 2015, Putin authorized Russian military intervention in the Syrian civil war on the side of President Bashar al-Assad — in contrast with American interests.

And, of course, Russian agents sought to influence the presidential election in 2016, according to U.S. intelligences services. So why do presidents continually believe they can succeed with Putin where others have failed?

“It’s the nature of American politics,” said Kaufman, the Pepperdine professor.

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Kaufman noted that Lyndon Johnson was convinced he could negotiate an end to the Vietnam War if only he could get North Vietnamese leader Ho Chi Minh alone in a room.

He said the same qualities that help presidents win elections sometimes lead them to exaggerate their capacity to change the course of foreign governments.

“To get there, you have to have a pretty healthy opinion about your persuasive abilities,” Kaufman said.

But Kaufman said that presidents’ domestic political skills often do not translate to foreign policy.