The early days of the 2020 Democratic presidential primary have been shaped by big policy debates on climate and criminal justice and reforms to democracy. That’s in part because there are 15 current and former members of Congress running for president. So it’s natural that legislation currently up for debate in Congress has been up for debate on the campaign trail as well.

Here’s a guide to some of the most common pieces of legislation you’ll hear about on the campaign trail and how they’re shaping the 2020 Democratic primaries.

STUDENT LOAN DEBT

Legislation you’ll hear talked about: The College for All Act

The basics: Introduced by Sen. Bernie Sanders (I-Vt.) on Monday, it would make tuition at public colleges free and get rid of all student loan debt, an estimated $1.6 trillion. Reps. Ilhan Omar (D-Minn.), Pramila Jayapal (D-Wash.) and Alexandria Ocasio-Cortez (D-N.Y.) support a similar bill in the House.

How it’s shaping 2020: Making public college free for everyone is a baseline policy for the more liberal members of the Democratic presidential primary. The next front is what to do about people already out of college who have student loan debt. Sanders’s plan is by far the most expansive. Sen. Elizabeth Warren (D-Mass.) and former Obama housing secretary Julián Castro want to get rid of some student loan debt. But moderate Democrats question whether the is the best way to spend taxpayer money is giving it to college graduates who tend to be high-earners later on in life.

ABORTION

Legislation you’ll hear talked about: The Hyde Amendment

The basics: This amendment, injected into must-pass bills since the 1970s, says the federal government cannot pay for anyone’s abortion. Practically, that means women on federally funded health insurance — the military, anyone who works for the federal government, lower-income people on Medicaid — can’t get an abortion covered (with some exceptions).

How it’s shaping 2020: There’s a divide between former vice president Joe Biden and everyone else in the field. Or, there was until Biden’s sudden shift on Thursday. In 2016, Democrats made repealing the amendment part of their party platform. But Biden, who says he personally opposes abortion but supports a woman’s right to choose, said this week he would keep the amendment. Then suddenly on Thursday, he told supporters he would oppose it.

Biden is leading by double digits in recent polls, so his opponents jumped at the chance to highlight how he supports an amendment more popular with Republicans than Democrats. It seems to have put enough pressure on Biden for him to do a 180 on his long-held position and put him in line with the rest of the primary field.

CLIMATE

Legislation you’ll hear talked about: The Green New Deal

The basics: It’s an ambitious — some say unrealistic — effort to make the United States a net-zero carbon emitter in a decade while funding Franklin Roosevelt-style social and economic justice programs, such as job training for those in the fossil fuel industry. Sen. Edward J. Markey (D-Mass.) and Rep. Alexandria Ocasio-Cortez (D-N.Y.) introduced the resolution this year, although House Speaker Nancy Pelosi (D-Calif.) is avoiding a vote in the House to protect her vulnerable members from accusations they support big-government, liberal policies.

How it’s shaping the 2020 debate: Few issues have taken on such urgency within the Democratic Party as action on climate change. Mitigating climate change stands near the top of Democratic voters’ priority lists, and the Green New Deal has become the gold standard for the party’s liberal base.

It’s now politically untenable for a Democratic Party contender to be seen as lax on climate change. Most of the top candidates have offered up proposals to spend trillions of dollars on clean energy and push the United States farther than it has ever gone toward reducing greenhouse gases. Biden released his own ambitious plan that mirrors the Green New Deal after Ocasio-Cortez — a powerful voice on the party’s left flank — criticized him as being too “middle of the road."

HEALTH CARE

Legislation you’ll hear talked about: Medicare-for-all

The basics: Medicare-for-all would create a national health-care program by enrolling all Americans in a government plan like Medicare, where they don’t have to pay co-pays or deductibles. (The program would be funded largely through taxes.) There are several versions of this, but in the Senate, Sen. Bernie Sanders (I-Vt.) has introduced a bill that would eliminate employer-sponsored insurance. Four of his competitors — Sens. Cory Booker (N.J.), Kirsten Gillibrand (N.Y.), Kamala D. Harris (Calif.), and Elizabeth Warren (Mass.) — have signed on. There have been two hearings on Medicare-for-all in the Democratic-controlled House, although Pelosi is not going to allow a vote anytime soon on it, lest it put her vulnerable members on the spot on yet another controversial bill.

How it’s shaping 2020: No issue underscores the debate in the Democratic Party about how far left it should go than the idea of having the government run the nation’s health-care system.

Sanders championed this while running for president in 2016, and now it’s mainstream in 2020. A Washington Post analysis finds 12 presidential candidates support some version of it, while eight prefer allowing people to buy into a government plan (rather than automatically enrolling them).

But some 2020 candidates are accusing the party of shooting itself in the foot with Medicare-for-all by making Democrats unelectable against President Trump, who has cast Democrats as socialists.

“Medicare-for-all may sound good, but it’s actually not good policy, nor is it good politics,” former congressman John Delaney (Md.) told a gathering of California Democrats recently. He got booed. “Socialism is not the answer,” former Colorado governor John Hickenlooper (D) said at the same event. He also was booed.

CRIMINAL JUSTICE

Legislation you’ll hear talked about: Two things — the 1994 crime bill and the 2018 First Step Act

The basics: In 1994 as a major Senate committee chairman, Biden championed a tough-on-crime bill that became law under President Bill Clinton. Some of the more controversial components gave states more money to build prisons and included a “three-strikes” provision that put drug offenders in jail for life with no parole. Experts say the bill was one contributing factor to the United States’ high incarceration rates.

More than 20 years later, Trump signed a federal prison reform bill into law that rewrote chunks of the ’94 bill to be less strict, notably the three-strikes provision. It was written by one of his Democratic rivals, Booker, and supported by every Senate Democrat running for president.

How it’s shaping 2020: This is an issue where a politician’s ideology is less important than the era the politician comes from. Biden is on the defensive about the ’94 crime bill from both sides.

“I disagree, sadly,” Harris said, challenging Biden’s assertion it didn’t “generate” mass incarceration.

“Anyone associated with the 1994 Crime Bill will not have a chance of being elected,” Trump tweeted.

Biden doesn’t talk much about this bill, although he has expressed regret for supporting sentencing disparities between crack and powder cocaine. African Americans were more likely to be convicted for selling or using crack and to be sentenced for longer terms, while offenses involving powder cocaine, a similar drug more often found in white communities, were punished less harshly.

REFORMS TO DEMOCRACY

Legislation you’ll hear talked about: Getting rid of the Senate filibuster; approving more Supreme Court justices than the nine currently on the bench; putting term limits on Supreme Court justices

The basics: These proposals are big changes to how government works, particularly the Senate. Right now any senator can filibuster legislation — except certain budgetary bills — and require 60 out of 100 senators to overcome the opposition. (Getting 60 senators is a rare occurrence in such a hyperpartisan Senate that’s divided closer to 50/50.) Getting rid of the filibuster would allow bills to be passed by a simple majority vote of 51 out of 100. (The Senate already recently got rid of the filibuster for judicial and political nominees, including Supreme Court nominees.) Some presidential candidates are also rethinking the Senate’s role in approving a president’s Supreme Court nominees to find ways for Democrats to get more leverage on a conservative court.

How it’s shaping the 2020 debate: Filibuster reform may sound esoteric, but it’s really a window into a much deeper Democratic divide over how to treat the Republican Party, says Molly Reynolds, a congressional analyst with the Brookings Institution: “They speak to the broader debate in the Democratic field about whether ‘things will go back to normal’ after Trump, or whether broader institutional reform and change are needed.”

The filibuster is also just one of several bold reforms to democracy that 2020 candidates are talking about: Should Election Day be a national holiday? Should the voting age we get rid of the electoral college, meaning the winner of the popular vote wins the White House? Should incarcerated felons be allowed to vote?

Sen. Elizabeth Warren (D-Mass.) has folded getting rid of the filibuster into her overall argument that Democrats need to play political and legislative hardball against Republicans: “We’re done having two sets of rules,” she has said.

Other candidates, such as Washington Gov. Jay Inslee, argue that undoing the filibuster is the only way Democrats can take action on big items that Republicans oppose, like acting on climate change.