Hillary Clinton and Bernie Sanders are in a pitched battle for the Democratic nomination, fighting for the hearts and minds of left-leaning voters across the US.
But where do they stand on the issues? While the candidates often agree on substance if not style, here's a look at five areas where they differ - not just from each other, but from their presidential predecessors, as well.
They will go up - but for whom?
Bernie Sanders promises he will reduce income inequality through changes to US through tax policy. He has called for a 10% tax surcharge on billionaires, raising the top three tax brackets and creating a new top rate, boosting capital gains and estate taxes, extending Social Security taxes, going after income made abroad by US corporations, and creating a new 0.2% tax on all earners to fund a paid family leave programme.
Hillary Clinton's tax plan is basically Sanders-lite. She wants a 4% surtax on income over $5 million, an increase in capital gains taxes, the closing of "tax loopholes" for the wealthy, taxing hedge fund managers' "carried interest" income at higher rates and increasing the estate tax rate.
Bill Clinton also raised taxes on the wealthy - and caught considerable criticism from conservatives for doing so. He instituted two new high-level tax brackets, raised corporate taxes, and increased income subject to Medicare and Social Security levies. After Republicans took control of Congress two years into his administration, he signed legislation lowering the capital gains taxes. He also increased a tax credit for poorer workers.
John F Kennedy was the original Democratic tax-cutter. He reduced the top rate in the US from 95% to 65% and the corporate tax rate from 52% to 47%. Today's conservatives love to quote his claim that a high tax rate "siphons out of the private economy too large a share of personal and business purchasing power".
Pitching college education that's free or just affordable
Bernie Sanders has set the bar when it comes to higher education policy in the modern Democratic Party, with his call for free college for all Americans funded by taxing Wall Street financial transactions. He points to the runaway costs of higher education as one of the driving forces behind growing income inequality in the US.
Hillary Clinton supports a plan to make two-year community college free, but her higher education policies are more modest. She has called for lowering student loan interest rates, providing $17.5 billion to improve the quality of higher education and encouraging colleges to set affordable tuition rates that don't require student loans.
Barack Obama signed legislation streamlining the student loan system, including provisions that allow the government to directly loan money to students rather than rely on for-profit middle-men. He has also proposed making the first two years of college free, with a programme modelled on a Tennessee system devised by the state's Republican governor.
Lyndon Baines Johnson is the godfather of the modern Democratic Party's education policies. As president he spearheaded passage of the Higher Education Act of 1965, which increased federal funding for universities and provided low-interest student loans and grants for needy students. It was landmark legislation in its day - but now seems relatively modest.
Mend it or end it - and start over from scratch.
Barack Obama supported and signed legislation increasing government regulation of the health insurance industry and creating private insurance markets for individuals not covered by employer-provided insurance. The programme was based, in part, on Republican proposals from the 1990s and the system instituted in Massachusetts by then-Governor Mitt Romney.
For Bernie Sanders, however, that particular half-loaf is far from enough. He wants to institute a single-payer government-run health insurance system fashioned on Medicare. He has also called for allowing the government to negotiate with pharmaceutical companies in order to lower prices and permitting Americans to import medication from Canada, where it is less expensive.
Hillary Clinton has said Mr Sanders is advancing an unrealistic proposal that threatens hard-won healthcare reforms made during Mr Obama's tenure. Instead she wants to expand existing law to improve coverage for prescription drugs and allow the government to negotiate with pharmaceutical manufacturers for better prices.
The former first lady does know a thing or two about how hard it is to get healthcare bills through Congress. In 1993 she was the driving force behind Bill Clinton's proposed legislation, which created a federal minimum-benefits healthcare package with limits on out-of-pocket expenses, all provided by regional healthcare alliances. That effort went down in flames before it even came to a vote in Congress.
The one place where Clinton comes at Sanders from the left
Hillary Clinton is the first prominent Democratic presidential candidate to openly run on a gun-control platform since Al Gore's losing campaign in 2000. She supports holding gun manufacturers liable for deaths caused by their products, expanding background checks and prohibiting those on no-fly list from purchasing firearms. She has also supported reinstating the ban on semi-automatic "assault" rifles.
Bernie Sanders, a senator from the rural state of Vermont, has a more moderate position on guns - although he has moved to the left over the course of the campaign. He supports expanded background checks on gun purchases and an assault weapons ban, but opposes holding gun manufacturers liable for deaths. He voted against a gun purchase waiting period multiple times in the early 1990s and for allowing guns in national parks.
Barack Obama shied away from campaigning on gun control in his two presidential campaigns, but the murder of schoolchildren in Newtown, Connecticut, in December 2012 convinced him to act. He has since called for an assault weapons ban and expanded background checks. He has taken unilateral executive action to increase enforcement of laws against gun trafficking and broadening the scope of federal regulation of firearm transactions.
Franklin Delano Roosevelt made the first serious effort at gun control by a Democratic president to date and his call in 1934 to create a national firearm registry and institute a federal tax on all gun purchases. No major Democratic officeholder would even consider broaching such a proposal today. It wouldn't just be dead on arrival in Congress, for many politicians it would be political suicide.
Remember the Iraq War? Bernie Sanders does.
Hillary Clinton, as secretary of state, was one of the more hawkish members of Mr Obama's cabinet. It's no surprise then that as a presidential candidate she is well to the right of Mr Sanders and even Mr Obama. She has called for greater US involvement in the Syrian civil war, including enforcing a no-fly zone, and supports a continued US military presence in Afghanistan.
Bernie Sanders generally agrees with Barack Obama's foreign policies - limited involvement in Syria and an emphasis on working with US allies. He contrasts himself with Mrs Clinton by noting the past US military action that she supported and he opposed - in Libya and Iraq. He supports a full US withdrawal from Afghanistan and no US training of rebels in the Syrian civil war.
John F Kennedy's foreign policy as president, compared to the current crop of Democratic politicians, seems downright bellicose. He was an interventionist at heart, authorising the Bay of Pigs invasion of Cuba, taking a hard line against Soviet expansion in the Western hemisphere and initiating US involvement in Vietnam.