This is the first in a four-part weekly series examining the dynamics of the new Congress.

The incoming House Democratic majority has an expanded liberal faction that is already making waves. The Progressive Caucus will grow to nearly 100 members next year, giving it tremendous potential influence. By comparison, the Freedom Caucus, the uber-conservative wing of the Republican Party, successfully blocked bills it didn’t like with only about three dozen members.

After the 2016 election, when Sen. Bernie Sanders (I-Vt.) energized a big segment of voters, Democrats began to consider whether they were better off pushing for boldly liberal policies. So, throughout 2018, many Democratic candidates embraced ideas like Medicare-for-all as they rode the wave of backlash to President Trump.

Now many of the candidates who did that — they call themselves progressives — are making their way to Washington. How will they shape it? Here’s what you should know about them.

What role will these liberals play? Will they get along with leadership?

The first test of whether the new left flank will get along with leadership came during House Democrats’ vote to nominate the next speaker. The progressives supported Minority Leader Nancy Pelosi (Calif.), whereas Freedom Caucus members didn’t always back the Republican caucus choice.

So far, the moderate Democrats have caused more headaches for leadership. They are most at risk when it comes to getting reelected, so they don’t want the party to skew too far left. But the liberals are likely to set the agenda and are unlikely to accept compromises with Trump and Senate Majority Leader Mitch McConnell (R-Ky.). For instance, Democratic negotiators agreed to appropriate $1.67 billion to fund Trump’s border wall (he wants $5 billion), but the progressives are insisting that the Democrats shouldn’t give anything. Democratic leaders face a difficult choice: whether to compromise to benefit more-vulnerable lawmakers or follow the party’s more liberal direction.

Who are the faces of the resurgent left?

The most high-profile incoming freshman in this group is Alexandria Ocasio-Cortez (N.Y.). She’s the youngest woman ever to be elected to the House, and she gained celebrity with her shocking upset of a longtime incumbent in a Democratic primary.

Minority women are the rising stars of the left. Ocasio-Cortez’s “squad” includes freshmen Ayanna Pressley (Mass.), Rashida Tlaib (Mich.) and Ilhan Omar (Minn.). They appear to be bonding with incumbent Rep. Pramila Jayapal (Wash.), who was just elected co-chair of the Congressional Progressive Caucus.

The 2020 presidential field will be crowded with candidates who consider themselves progressives, like Sens. Elizabeth Warren (D-Mass.) and Sherrod Brown (D-Ohio), as well as Sanders, whose last campaign’s impact was so great that those who share his views are often referred to as the “Sanders wing” of the party.

What do they care about?

The left has some big-ticket items they want, like the “New Green Deal,” which would create a committee to develop ideas to move the country to 100 percent renewable energy within the next decade, and Medicare-for-all, a universal health system modeled after the Medicare program. Expect the group to push for immigration reform with a path to citizenship and free college tuition.

Will they pull their party left as it relates to 2020?

Some of the ideas the new liberal faction in Congress puts forward may end up being litmus tests for the couple dozen Democrats eyeing a run for president.

They have support from many grass-roots organizations, and they’re hoping to tap into them to pressure 2020 candidates to adopt big liberal ideas. Already top Democratic contenders have sworn off donations from Corporate PACs. Now that the media is watching, they will see how far left they can push Democratic leadership. Currently, the party is divided over whether it needs a presidential candidate who pushes a liberal agenda or a more moderate politician who can appeal to voters in the South and the Midwest.