The liberal wing of the Democratic caucus in the U.S. House is going to be bigger than ever when the new Congress starts in January. It’ll be much larger than the conservative wing, and that has major implications, both for the next two years and potentially for 2021.

“Duh,” you might say, “of course there are more liberal than conservative Democrats.” But the two wings used to be much more equally matched. And 2018 represented a big jump in the progressive ranks.

In 2010, when Democrats last controlled the House, there were 80 House members in the Congressional Progressive Caucus, a bloc of the most liberal members of the House and Senate, according to a caucus spokesperson. The Blue Dog Coalition, a group of the most conservative House Democrats, stood at 54 members. And the conservatives rivaled the liberals in influence. The Affordable Care Act, for example, grew more conservative in a number of ways thanks to pressure from conservative Democrats.

But many of the Blue Dogs back then represented more conservative-leaning areas, particularly in the South. Between 2010 and 2016, more than two dozen of them either lost re-election bids or retired from the House (often anticipating defeats). Even amid the Democratic wave this year, the number of Blue Dogs will likely only grow from 18 to 24. (More newly elected members could join the Blue Dogs later.) Meanwhile, the Progressive Caucus ranks held steady during the Obama years (these members tend to be in fairly liberal districts), so the group stood at 78 members before the 2018 midterms. That number will grow to 96 in 2019, according to the group, as a number of progressive candidates won in previously Republican-held districts.

Put another way, in 2010, there were about 1.5 progressives for every Blue Dog in the House. In 2019, progressives will have a 4-to-1 advantage. This is the biggest the Progressive Caucus has ever been, according to a spokesperson for the group.

Why does all this matter? After all, liberal policies like Medicare-for-all are almost certainly not going to be signed into law as long as Donald Trump is president and Republicans remain in control of the Senate. That’s true enough, but some legislation — most notably bills to fund the federal government — must be approved over the next two years, divided government notwithstanding. Ultimately, those bills will be hashed out in negotiations led by Senate Majority Leader Mitch McConnell, President Trump and whoever leads the House (likely Nancy Pelosi). But the bills will have to be approved by the full House and will likely need a lot of Democratic members backing them.

I don’t think the progressives are going to just placidly follow Pelosi’s lead and vote for whatever she negotiates with Trump and the Republicans in the Senate. Instead, I expect the group to push the party to the left in these negotiations. In some ways, the progressives in 2019-20 could act a lot like the House Freedom Caucus did in 2017-2018. The Freedom Caucus, a bloc of the most conservative members of the House, often successfully forced House Speaker Paul Ryan to make bills more conservative. Democratic leaders in the Senate, for example, were hinting earlier this year that they would agree to fund Trump’s border wall in exchange for a provision basically turning the Deferred Action for Childhood Arrivals program into a federal law. Trump didn’t take the deal, so it never came to a vote. But I don’t think that kind of deal will be much of an option going forward — progressive Democrats are unlikely to view such a compromise favorably, and would likely fight to limit any wall funding. (Some of them were pushing a provision earlier this year to abolish the Immigration and Customs Enforcement Agency.)

All these fights will help set the Democratic agenda for the future. There is a very real chance that a Democrat will be elected president in 2020, and that that victory would come with a Democratic House and maybe even control of the Senate. So House Democrats are likely to consider, draft and pass bills in 2019 and 2020 that will go nowhere right now, but would provide a blueprint for a 2021 agenda, if Democrats control both chambers of Congress and the presidency. This is what Republicans did during the Obama years. The repeal of the Affordable Care Act that passed the House in 2017 wasn’t a new idea: House Republicans had approved such a proposal when Barack Obama was president, even as they knew he would veto it.

So now is the time for the Progressive Caucus to start pushing the Democrats to adopt more left-leaning ideas. And they are already starting to do that — even before the new Congress starts. For instance, New York’s newly elected Alexandria Ocasio-Cortez and other House progressives are calling for a “Green New Deal,” an aggressive, comprehensive proposal to address climate change. The progressives are also opposing a Pelosi initiative to require a three-fifths majority in the House to pass any bill that would raise income taxes on any Americans except the wealthiest 20 percent. That rule, the progressives argue, could hamstring Democrats if they want to pursue more aggressive proposals, like free college or Medicare-for-all.

What might limit the progressives’ influence? Well, University of Chicago political science professor Ruth Bloch Rubin, author of a 2017 book on congressional caucuses, argues the group might be too big.

“The Blue Dogs may now be dwarfed by the Progressive Caucus, but historically they have been much better organized, and thus in a better position to credibly bargain with party leaders and threaten to defect from the party line as a bloc,” she said.

“The comparison to the Freedom Caucus reveals the same dynamic. The Freedom Caucus when the Republicans were in the majority deliberately chose to keep their size down …. The Progressive Caucus doesn’t have a similar barrier to entry, and this may mean that some opportunists will join but ultimately won’t share the hardcore progressive ideals of their colleagues,” she added.

I think Bloch Rubin is right — this bloc will be hard to organize, and it will be tough to get everyone behind one position at the same time. That said, the progressives in the House are part of a broader tide moving the party to the left: More Democratic voters are identifying themselves as liberal; a huge swath of the party’s politicians are embracing Medicare-for-all; fairly liberal candidates are running and winning, even in traditionally conservative areas. The liberals in the House are very likely to push their colleagues left. The only question is how far.