Sen. Bernie Sanders of Vermont, now a presidential candidate, is the only socialist in Congress. But "he's a 'small S' socialist," professor Garrison Nelson of the University of Vermont told me last year. "He's not, 'Let's totally revamp the government, break up the corporations, create five-year plans.' He doesn't get out too far on an ideological limb."

Sanders resembles many in the Democratic Party by criticizing the excessive influence of the wealthy. But he takes things much further, both rhetorically and substantively — he thinks checking the power of billionaires and corporations is the defining issue in US politics today. He's most interested in economic issues, from inequality to trade, and as a result he's won a devoted following among liberals who think their party too frequently carries water for the rich.

But while Sanders wants a single-payer health care system, a carbon tax, and much more government spending on infrastructure and benefits, he isn't an uber-liberal on everything. On social issues like abortion, gun rights, and gay rights, he is squarely within the mainstream of the Democratic Party — not to its left. And while he's suspicious of foreign wars, he voices sympathy with Israel's security concerns and warns of the dangers of ISIS. Here's a guide to his views.

Move to a single-payer health care system

The major issue on which Sanders embraces "full socialism" is health care, where he maintains his longtime support of a single-payer health-care system. At an Iowa event last year, Sanders called Obamacare a "modest step forward." But he said much more work needed to be done on expanding coverage and reducing the costs of care: "We are the only major nation on earth that does not guarantee health care to all people." The problem, he said, is that in the current system, "the goal is for the insurance companies and the drug companies to make as much money as possible."

Sanders was a key supporter of Vermont's plan to implement the United States' first single-payer health care system. "If we do it and do it well, other states will get in line and follow us," he said. "And we will have a national system." But the plan has since foundered over cost concerns, and implementation has been indefinitely postponed. "It's not that it hasn't worked out, it hasn't been implemented," Sanders told The Hill this February.

Overturn Citizens United, publicly fund elections

Sanders has harshly criticized Supreme Court rulings allowing for increased spending on elections by individuals and outside groups. "We must pass a constitutional amendment to overturn the disastrous 5-4 Citizens United Supreme Court decision," he's said. "Billionaires like the Koch brothers should not be able to spend hundreds of millions to buy elections in the US." He's also called for moving toward public funding of elections, saying, "We are losing our democracy in this country."

Free trade's expansion has been a "disaster"

"Unfettered free trade has been a disaster for the American people," Sanders told me. "It was pushed by corporate America with many Democrats including Bill Clinton and the Republicans working to support him." He said that during his two and a half decades in Congress, "I voted against all the trade agreements." He has been harshly critical of the Trans-Pacific Partnership, and will make his opposition to it a key feature of his campaign.

Combat climate change with a carbon tax

"Global warming is the greatest environmental threat facing the planet," Sanders has said, "and averting a planetary disaster will require a major reduction in the burning of coal, oil, and other fossil fuels." To that end, he supports a carbon tax, which he calls "the most straightforward and efficient strategy for quickly reducing greenhouse gas emissions."

Don't cut Social Security — expand it (by taxing the wealthy more)

Sanders scoffs at the idea that the US faces a deficit problem that necessitates cuts in benefits or domestic spending. He mocks "entitlement reform" as a "code word" meaning "cutting Social Security and Medicare," and fought against President George W. Bush's proposal to partially privatize Social Security in 2005.

For Social Security in particular, Sanders says improved benefits could be funded by simply increasing payroll taxes on the rich. He's suggested applying the tax to all income over $250,000 a year. "You do that, you bring in enough money to extend Social Security for decades — and you also give us the resources to expand benefits, not cut them," he said at an event in Waterloo, Iowa, last year.

More spending on infrastructure, less on defense

Sanders has proposed spending $1 trillion on modernizing infrastructure, saying it would both put people to work and generate more economic activity. As for deficits, he wants big cuts in military spending, saying, "It is absurd that the United States continues to spend almost as much on defense as the rest of the world combined." He's frequently suggested that any increases in defense spending should be fully funded by tax increases on the wealthy.

Don't tax the middle class more — they're already getting squeezed

As seen above, Sanders has frequently called for greater taxation of the wealthy. However, despite proposing a great deal of increased spending, he has not called for tax increases to the middle class or low-income people to fund these efforts.

Instead, he generally argues that the middle class is already getting squeezed — his speeches tend to include a blizzard of statistics about growing inequality. "The most significant issue facing this country is the 40-year decline of the American middle class," he's said.

Raise the minimum wage quite a lot

"If we are going to be serious about cutting poverty," Sanders said in a speech last year, the minimum wage should be raised "to a living wage." He supports raising it from the current level of $7.25 to $10.10 an hour, but says "that is not enough," and wants more of an increase "in the coming years."

Supports immigration reform — but not guest worker programs for unskilled labor

Sanders supports a pathway to citizenship for unauthorized immigrants here now, and voted for the Senate's 2013 immigration reform bill. However, he criticized the bill's expansion of guest worker programs, particularly those involving unskilled workers. "I'm very dubious about the need to bring foreign unskilled labor into this country," he said in 2013. "What I do not support is, under the guise of immigrant reform, a process pushed by large corporations which results in more unemployment and lower wages for American workers."

Does not support drug legalization

"I have real concerns about implications of the war on drugs," Sanders told Time in 2014. He said it's lasted decades, to "a huge cost and the destruction of a whole lot of lives of people who were never involved in any violent activities." But he added that especially considering Vermont's heroin epidemic, "I am concerned about the overuse of dangerous drugs." Asked about marijuana legalization, Sanders said he'd "look at it," but that "to me it is not one of the major issues facing this country."

Label foods with GMO ingredients

Sanders strongly supported Vermont's law requiring labels on foods with genetically engineered ingredients — the first such law in the nation. Vermont's law is facing a court challenge, but Sanders has proposed federal legislation to ensure states can pass labeling laws. He has said that "a movement to allow the people of our country to know what is in the food they eat" is standing up to "Monsanto and other multinational food conglomerates."

Supports more gun control — but hasn't always

Sanders has been a consistent supporter of laws to toughen gun control in recent years. But earlier in his career, he was hesitant to engage on it — likely reflecting his rural constituents' views. He voted against a bill requiring a waiting period for a handgun purchase in 1991, calling it "symbolism" and saying gun control shouldn't be a federal issue. However, in 2013, Sanders voted for the Democrats' post-Newtown gun control bill, which expanded background checks and restored the assault weapons ban. He said there was "a growing consensus" that "we have got to do as much as we can to end the cold-blooded mass murders of innocent people."

Much more government funding for higher education

Frequently, Sanders argues for the importance of making college affordable. "Because of the high cost of higher education, many bright young people can no longer afford to go to college, and millions of others are leaving school saddled with debt. This is absurd," he's said. At an event last year, he said it's "time we thought about" making college free for everyone. As a first step, he's suggested that there should be no tuition for the first two years for any public college or university, saying, "We need a revolution in the way higher education is funded."

Less foreign policy interventionism

Sanders is a critic of most large-scale military interventions abroad, saying they are frequently expensive and counterproductive. He opposed the Iraq War, says Republicans are now "itching" for a war with Iran, and said he had "reservations" about Obama's intervention in Libya.

"ISIS is a brutal, awful, dangerous army and they have got to be defeated," he said last year. But, he added, "this is not just an American problem," and called on Arab nations to take the lead in the fight. "This is a war for the soul of Islam and the Muslim nations must be deeply involved."

Stop the NSA's "out-of-control" surveillance

"The National Security Agency and other intelligence agencies are out of control," Sanders has said. " We cannot talk about America as a 'free country' when the government is collecting information on virtually every phone call we make, when it is intercepting our emails and monitoring the websites we visit. That is not what a free society is about." He was one of the few members of Congress to vote against the first version of the Patriot Act, back in 2001.

Supports abortion rights and same-sex marriage

Sanders is pro-choice, and he has long been a supporter of LGBT rights. He voted against the Defense of Marriage Act, which was signed into law by President Clinton in 1996. He backed Vermont's civil unions law in 2000 and its full marriage equality law in 2009.

Network neutrality is essential for free speech

Sanders strongly supports efforts to preserve network neutrality. "Our free and open internet has made invaluable contributions to democracy both here in the United States and around the world," he has said. "We must not let private corporations turn bigger and bigger profits by putting a price tag on the free flow of ideas."

Reform the Export-Import Bank

Sanders has long been a critic of the Export-Import Bank, as David Dayen documents at Salon. In a 2002 speech, Sanders asked why US taxpayers should give "huge subsidies and loans to the largest multinational corporations in the world, who pay their CEOs huge salaries … and companies take this money from the taxpayers and say, thank you very much, and oh by the way, we are laying you off because we are going to China and hiring somebody at 20 cents an hour." He voted against reauthorizing the bank in 2014.

READ MORE: Bernie Sanders vs. the billionaires