Russian President Vladimir Putin told reporters during his annual end-of-year news conference that he welcomes calls by U.S. Republican presidential frontrunner Donald Trump for deeper relations with Russia. He says Trump is the man to watch. (Reuters)

Perhaps it should come as no surprise that Vladimir Putin supports Donald Trump. The American billionaire has spoken glowingly of the Russian leader, and the pair share a style of politics that often hinges on insults and other displays of power.

Even so, Putin's informal endorsement of Trump on Thursday during a lengthy news conference – in which the Russian president said he would welcome a Trump presidency and declared the Republican hopeful the “absolute leader in the presidential race" – could prove controversial among American voters.

Over the past few years, Putin has emerged as a pariah on the world stage, criticized widely for pursuing an aggressive policy first in Ukraine and now in Syria. While there are certainly elements of the Republican Party who look at his leadership with respect, few mainstream politicians from either party have kind words for him – GOP presidential candidate Marco Rubio, for example, has dubbed the Russian president a "gangster."

But do American voters actually care about what controversial foreign leaders think? Let's look at a few other informal endorsements over the past years.

2004: North Korea supports John Kerry

As he faced off against President George W. Bush in 2004, John Kerry bragged of his informal endorsements from behind the scenes. Unfortunately, the support of North Korean leader Kim Jong Il wasn't kept secret. According to the Financial Times, Kerry's speeches were broadcast on North Korean state radio, and reports of his campaign were written about approvingly by Korea Central News Agency (KCNA).

Kerry went on to narrowly lose the election.

2004: Vladimir Putin supports George W. Bush

That same election, Putin would offer his own support for Bush, justifying it with his support for the Republican incumbent's fight against terror. "International terrorists have set as their goal inflicting the maximum damage to Bush, to prevent his election to a second term," Putin told reporters. "If they succeed in doing that, they will celebrate a victory over America and over the entire anti-terror coalition."

By this point, Bush had already expressed his admiration for the Russian leader, telling reporters he had looked into his eyes and had seen his soul. Bush went on to win the election.

2008: A Hamas adviser supports Barack Obama

Ahead of the 2008 election, Ahmed Yousef, a chief political adviser to Hamas, told WABC Radio that the Palestinian political organization "liked" Barack Obama and that he believed the Democrat was like "John Kennedy, a great man with great principles." While it was far from a formal endorsement by the group, the comments spread widely throughout the media and were even picked up by Obama's Republican opponent in the presidential race, John McCain.

Despite this attention, later in the campaign a Hamas official told Reuters that they did not support Obama and that they had no preference in the election.

2008: Al Qaeda (kinda) supports John McCain

The New York Times' Nicholas Kristof called it the "endorsement from hell."

In 2008, not long before the election, a commentary on a secretive Islamist website said that "Al Qaeda will have to support McCain in the coming election." There was no official follow-up from the terrorist organization, but the comments seemed to suggest that terror groups felt the Republican's hawkish policies were their best chance to find more recruits and continue to wage war on the United States.

McCain went on to lose the election to Obama.

2008 and 2012: Hugo Chavez supports Barack Obama

On the eve of the 2008 presidential election, Venezuelan leader Hugo Chavez offered some limited support for Obama, praising the "arrival of a black president to the United States."

While the two leaders would later go on to have an antagonistic relationship after Obama took office, Chavez always had something of a soft spot for Obama. In the 2012 election, he reaffirmed that, telling reporters that if he was American he would vote for Obama. "Obama is a good guy ... I think that if Obama was from Barlovento [a predominantly black coastal town in Venezuela] or some Caracas neighborhood, he'd vote for Chavez," the president told state TV.

2012: Muammar Gaddafi endorses Barack Obama

Just after Obama's reelection campaign began in April 2011, Libyan dictator Muammar Gaddafi released a letter openly endorsing him – and asking that the U.S. president halt the bombing campaign against him.

"We Endeavour and hope that you will gain victory in the new election campaigne [sic]," the letter, addressed directly to Obama, read. "You are a man who has enough courage to annul a wrong and mistaken action."

While Obama did go on to win the campaign, it was of little help to Gaddafi: He was captured by rebel forces and killed just a few months later, over a year before the election actually took place.

2012: Benjamin Netanyahu endorses Mitt Romney

Israeli Prime Minister Benjamin Netanyahu seemed to bet on the Republican presidential candidate in 2012, receiving his old friend Mitt Romney in his Jerusalem home for a dinner. His criticism of Obama also appeared in some conservative election advertisements airing in Florida.

Unfortunately for Romney, this didn't seem to sway the election. And for Netanyahu, it likely further strained his already difficult relationship with Obama.

2012: Vladimir Putin supports Barack Obama

The Russian leader hasn't always been a fan of Republicans. Following a series of comments made by Romney in 2012 that disparaged Putin's leadership of Russia, Putin seemed to offer his support to the Democratic incumbent. Speaking to RT television, Putin suggested it would be hard to work with Romney if he won office, and added that Obama was "an honest person who really wants to change much for the better."

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