After putting up a tough fight against the eventual 2016 Democratic presidential nominee, Hillary Clinton, Sen. Bernie Sanders, I-Vt., is one of the front-runners for the party's 2020 nomination to take on President Trump.

Here are five things to know about him as the 2020 presidential election cycle is officially underway.

1. He's an independent in the Senate

Sanders' official party affiliation in the Senate is as an independent, though he caucuses with the Democrats. The self-declared democratic socialist is one of the most liberal members of Congress, at times bucking Democratic leadership when it works with Republicans on moderate legislation.

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"I am an independent and I have always run in Vermont as an independent, while I caucus with the Democrats in the United States Senate. That’s what I’ve been doing for a long time and that’s what I’ll continue to do,” Sanders said in the interview as he announced his 2018 reelection campaign to the Senate.

Sanders does, however, have good relationships with many Democrats and a lot of supporters in the Democratic base, which is a good thing for him as it's almost impossible to win a national election while representing a third party.

2. He's released a folk album

Sanders, who was the mayor of Burlington, Vt., before making his way into the House of Representatives and eventually the Senate, in 1987 released a political folk album with the help of a producer and a group of Vermont musicians.

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Its tracks include "We Shall Overcome," "This Land is Your Land," "Oh Freedom" and others.

3. He had a heart attack in 2019

Sanders suffered a heart attack in October, as the presidential campaign was well underway. He seemed to recover quickly, however, and was back on the debate stage later that month.

Sanders released his medical records in December, which included a note from his doctor that said, "You are in good health currently and you have been engaging vigorously in the rigors of your campaign, travel, and other scheduled activities without any limitation,”

4. The 78-year-old is endorsed by some of the youngest members of Congress

At 78 years old, Sanders is older than fellow septuagenarian presidential candidates Trump, Sen. Elizabeth Warren, D-Mass., and former New York City Mayor Michael Bloomberg. But Sanders has snagged endorsements from 75 percent of the "Squad," a high-profile group of young, freshman congresswomen who are part of a larger effort to drag the Democratic party to the left.

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Reps. Alexandria Ocasio-Cortez, D-N.Y., Rashida Tlaib, D-Mich., and Ilhan Omar, D-Minn have all endorsed Sanders' campaign for president. Fellow 'Squad' member Rep. Ayanna Pressley, D-Mass., endorsed Warren, her home-state senator.

5. He honeymooned in the Soviet Union

On his honeymoon to the Soviet Union in the 1980s, Sanders apparently bashed the United States to an extent that one of his fellow travelers needed to walk out of the room.

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“I got really upset and walked out,” David F. Kelley, a Republican who helped arrange the trip and was part of the entourage, recalled in an extensive piece in The Washington Post. Kelley said that during Sanders' 1988 trip, the now-2020 presidential hopeful acted inappropriately by criticizing his own country amid the Cold War.

Sanders has also praised Cuban dictator Fidel Castro and Nicaraguan socialist leader Daniel Ortega in the past, in addition to defending bread lines in socialist countries.

Fox News' Paul Steinhauser, Andrew Craft and Sam Dorman contributed to this report.