WASHINGTON — As Democrats prepare to push their agenda in the House and kick off the 2020 presidential campaign, progressive policy ideas that came to the fore this year are going to come under the microscope like never before.

Once-obscure causes like abolishing ICE or the Green New Deal went viral among the grassroots, with help from rising stars in the party. Older proposals like single-payer health care broke into the mainstream and drew wider support from elected officials. Democrats weighing presidential runs unleashed a barrage of far-reaching bills of their own, from sweeping ethics legislation to giant tax cuts.

Expect major debates not only over how far the party should go, but how it should prioritize so many ambitious demands. Here are some of the policy fights to watch:

GREEN NEW DEAL

Riding into Washington as a phenomenon among young progressives, Rep.-elect Alexandria Ocasio-Cortez, D-N.Y., immediately started putting her political capital to use by backing protesters calling for a Green New Deal.

The deal isn't fully defined, but activists are generally seeking large-scale investments in renewable energy and a plan to implement them rapidly. As a first step, they've demanded that the House restart a select committee on climate change and come up with a blueprint to slash carbon emissions within a decade.

Rep. Nancy Pelosi, D-Calif., the House minority leader and speaker nominee, is supportive, but the select committee's role in relation to other Democrat-led committees could be a source of tension.

While not mutually exclusive, the movement in some ways rivals calls for a carbon tax to address climate change. Sens. Jeff Flake, R-Ariz., and Chris Coons, D-Del., unveiled a bipartisan bill for a revenue-neutral tax on emissions in December, pointing to another possible direction. With France convulsed by protests over a fuel tax, the debate over how to respond to climate change without enraging voters is going to be even more heated in 2019.

The Republican pushback: Trump has openly derided climate science, pulled out of the Paris climate agreement and has a long intensely personal grudge against wind energy, so don't expect the White House to back down. There's still very little appetite for significant action on climate change among elected officials and their voters on the right, with politicians frequently deriding regulation and bills to confront the issue as a drag on business.

MEDICARE FOR ALL

No policy idea has captured the left's imagination — and picked up more support within the party — like Medicare For All in recent years. Jumping off the momentum of Sen. Bernie Sanders' presidential run in 2016, activists have helped gather 124 co-sponsors for single-payer legislation in the House and 16 in the Senate.

But with Democrats taking control of the House and presidential candidates gaming out their platform, 2019 will be the biggest gut check yet for how much backing the idea has in practice.

Sen. Bernie Sanders speaks in Jackson, Mississippi, on April 4, 2018. Rogelio V. Solis / AP file

While the party has moved left on health care, many Democrats seem more comfortable offering an option to buy into Medicare or a similar public plan rather than creating one single-payer plan that replaces private insurance and covers everyone. Progressives, led by Rep. Pramila Jayapal, D-Wash., and her Medicare For All PAC, plan to whip up support for the maximalist version and advance legislation in 2019.

Expect plenty of high-profile clashes on the topic next year, both between the parties and within them.

The Republican pushback: During the midterms, Republicans in competitive races often seemed more eager to talk about single-payer than Democrats. Common criticisms of Medicare For All included its elimination of private insurance, its estimated $32 trillion cost and insinuations that its beneficiaries would compete with seniors on Medicare for funding and attention from doctors. But the GOP's attacks on it failed to prevent major losses and Republicans are still stuck in a tough place on health care as the president and his allies sue to repeal Obamacare, including some of its most popular features.

ABOLISH ICE

The spread of "Abolish ICE" showed how fast an idea can spring up from anywhere, rise to prominence online and turn into actual legislation on the Democratic side and attack ads on the Republican.

Immigration activists had long protested ICE's deportations dating back to its founding in 2003, but their demands became crystallized in a slogan by Data for Progress co-founder Sean McElwee, who relentlessly promoted "Abolish ICE" on social media.

Within months, Democratic candidates were getting grilled on the concept and some were rushing to take ownership of the idea and translate it into policy. Rep. Mark Pocan, D-Wis., co-chair of the Progressive Caucus, worked on a bill that would fold ICE's operations into other agencies.

There will be plenty more discussion in 2019 about how Democrats balance demands from the grassroots on immigration with border security concerns from swing voters.

Demonstrators march through downtown calling for the abolition of the U.S. Immigration and Customs Enforcement (ICE) in Chicago, Illinois on August 16, 2018. Scott Olson / Getty Images file

The Republican pushback: Not every Democrat was happy about Abolish Ice's emergence, especially as the midterms neared. President Donald Trump started attacking the slogan as evidence that Democrats would tolerate illegal immigration and favored "open borders," and some vulnerable members like Sen. Joe Donnelly, D-Ind., ran ads distancing themselves from the concept. In Kansas, Rep.-elect Sharice Davids expressed support for the Abolish ICE movement in an interview then walked it back.

CORPORATE 'WARFARE'

Democrats have looked to reclaim the populist mantle against Trump, but there are still plenty of arguments over how best to do so.

Sanders has been the leading evangelist for a tactic that emphasizes calling out individual corporations by name with messaging bills that are designed to get under a CEO's skin even if they're unlikely to pass. His Stop BEZOS Act, with Rep. Ro Khanna, D-Calif., would have charged companies for employees whose wages qualified them for public services like food stamps.

Jeff Bezos, CEO of Amazon, speaks during a press conference in this Sept. 6, 2012 file photo in Santa Monica, California Joe Klamar / AFP - Getty Images file

The bill drew intense criticism from economists, including prominent progressives, who said it was poorly designed and would lead to job discrimination against the poor. But it also drew further attention to Amazon's worker practices. CEO Jeff Bezos eventually announced he was raising wages to $15 an hour and he and Sanders exchanged some kind words in response.

Expect plenty of related bills to get attention in 2019. Democrats have largely united behind a $15 minimum wage, but the details and timetable could be contentious if the new Congress tries to pass a bill. Sen. Elizabeth Warren, D-Mass., has been pushing legislation to give workers a share of seats on corporate boards, an idea that’s also gained steam on the left. And Sanders is already moving onto a new target: His new Stop WALMART Act would force companies who buy back their own stock to also pay their employees $15 an hour.

The Republican pushback: Conservatives have long opposed the $15 minimum wage, pointing to studies (disputed by other researchers) that suggest higher minimum wages reduce total employment. In Michigan, Republicans even passed legislation scaling back a voter-passed minimum wage increase. But there is some rhetorical overlap between Trump's brand of populism and Sanders' in that both are unusually willing to criticize individual CEOs and companies.

MONEY, MONEY, MONEY

A growing number of 2020 potential candidates are proposing bills that would directly transfer cash to Americans via tax cuts or a new type of benefit.

Sen. Kamala Harris, D-Calif., has the LIFT Act, which would give checks of up to $500 to families making up to $100,000. Sen. Sherrod Brown, D-Ohio, has the GAIN Act, which would massively expand the Earned Income Tax Credit in size and income range. And Sen. Cory Booker, D-N.J., has the American Opportunity Accounts Act, which would give every American a $1,000 "baby bond" at birth that acquires interest and adds more deposits each year depending on family income.

U.S. Sen. Kamala Harris, D-Calif., speaks at the "Families Belong Together: Freedom for Immigrants" March in Los Angeles on June 30, 2018. Willy Sanjuan / AP file

There's skepticism on the left about these bills. Some progressives are resistant to spending trillions on legislation that subsidizes incomes they think employers should raise on their own. How to prioritize these plans versus big programs like Medicare for All, free college or a jobs guarantee is likely to be an ongoing argument. But it’s worth keeping on eye on whether they might become more prominent in 2019 as an answer to the Trump tax cuts.

The Republican pushback: There's a reason these kinds of tax cuts didn't make it into the Republican bill beyond a modest boost to child tax credits. Cutting taxes on corporations and high earners is the bigger priority on the right, which they say will spur greater economic growth, and it costs a lot to do. There's also ideological opposition among many conservatives to refundable tax credits.