Democratic Senator Claire McCaskill, who is up for reelection in the red state of Missouri in 2018, recently told a St. Louis radio host she may face a primary challenge. “I may have a primary because there is, in our party now, some of the same kind of enthusiasm at the base that the Republican Party had with the Tea Party,” she said during an interview earlier this month. “Many of those people are very impatient with me because they don’t think I’m pure,” she added.

As the Democratic Party contemplates what’s next in the wake of its defeat in the presidential election, liberals may have to decide what matters more: Building a big tent party where far-left voters and moderate centrists can co-exist even if they occasionally disagree on policy and strategy, or focusing on the demands of the party’s progressive base, potentially creating a more like-minded and ideologically rigid coalition in the process.

In an effort to persuade Democrats to embrace a big-tent strategy, Third Way, a center-left think tank, argues in a new report that voters aren’t necessarily rigidly attached to a particular party, and might be won over as a result. The report, titled “Why Demography Does Not Equal Destiny,” concludes that demographic change in the United States won’t deliver Democrats a winning electoral coalition by default, but that there are still opportunities for the party to convince Americans to vote for Democratic candidates even if they haven’t always done so in the past.

“There are definitely persuadable voters out there and the question we should be asking right now is: ‘Who can be persuaded to embrace our vision of the future?’” report co-author Lanae Erickson Hatalsky of Third Way said in an interview. “The idea that there was this rising electorate that would automatically deliver progressive victories wooed us away from doing the hard work of trying to find common ground with people since it seemed easier to just find people who agreed with us.”

Erickson Hatalsky argues that voting trends suggest that some voters swing back and forth between the two parties rather than remain consistently loyal to one party or the other. For example, hundreds of counties across the United States flipped from voting for Barack Obama in the 2012 presidential election to voting for Trump in 2016. Some congressional districts also delivered victory for Trump while at the same time reelecting Democratic members of Congress, like Cheri Bustos in Illinois and Matt Cartwright in Pennsylvania.

“There are clearly people out there who have not decided that they vote for only one party,” Erickson Hatalsky said. “I think that’s hopeful because it indicates that if the Democratic Party takes the time to listen to what it is that these people are looking for, we may be able to expand our coalition.”

The report notes that there has been a rise in the number of voters who identify as independent in recent years, and suggests that they could be a potential target for the Democratic Party. Some political scientists, however, maintain that independent voters are really partisans in disguise—people who may not want to publicly identify as a Republican or a Democrat, but nevertheless consistently vote for candidates of a particular party. Third Way has challenged this conclusion, and does so in the report by tracking how independents have swung as a voting bloc back-and-forth between voting for Democrats to Republicans in presidential elections dating back to 1976.

“Independents lean toward one party or another, and vote for that party, over shorter time horizons, but this trend shows that over longer time horizons partisan loyalties are not fixed in place for independent voters,” Erickson Hatalsky said.

But what if there isn’t a significant number of voters available for Democrats to win over or win back? What if, instead, the partisan battle lines are now firmly entrenched, and spending time, energy, and effort trying to change hearts and minds proves to be a losing proposition for the party?

Alan Abramowitz, a political scientist at Emory University, is skeptical that Democrats can significantly grow their base by converting large numbers of either Republicans or Trump voters. He believes Democrats would be more effective if they focused on increasing turnout of core Democratic constituencies, such as African American, Hispanic, and younger voters.

“There’s a reason why campaigns are devoting more and more resources trying to energize the base rather than trying to persuade people. It’s because trying to persuade people is extremely difficult in this day and age,” Abramowitz said in an interview. “That’s not to say there won’t ever be any movement back and forth between parties,” he added, “but I just don’t see there being any large number of movable voters.”  

Abramowitz notes that looking back at the voting behavior of independents spanning the past several decades may fail to adequately recognize that party loyalties are much stronger today than in the 1970s and 80s. Instead, he points to increasing ideological division among voters in recent years and what he calls “negative partisanship”—a phenomenon whereby animosity toward the opposing party becomes a driving factor behind how a person decides to vote—to argue that there likely isn’t a significant number of voters up for grabs.

Erickson Hatalsky acknowledges “there’s little evidence to suggest there’s a whole swath of Democratic voters sitting at home who are just waiting to come out if we excite them.” But, she added, “if we are going to build a progressive coalition that can dig Democrats out of their hole at the state and local level and get them back into the White House, we can’t write people off either. Voters who went for Obama and then Trump cannot be deemed unreachable for Democrats, and neither can voters in states that voted for Trump, but have continued to elect Democrats to Congress. To do so, is to accept permanent status as a coastal, urban, powerless party.”

As the centrist wing of the Democratic party attempts to make its case, it will have to contend with an increasingly restive progressive base. A wave of protests across the country—including the Women’s March and rallies in opposition to the first iteration of President Trump’s travel ban—seem to have convinced at least some Democrats in Congress to become increasingly uncompromising in their opposition to the president’s priorities. Progressives are also organizing in the aftermath of the election with the explicit aim of launching primary challenges against Democrats they deem not rigid enough in their opposition to Trump.

If centrist Democrats want to ensure that the Democratic Party embraces a big-tent strategy, they will need to convince skeptical voters of the merits of the party. They  may also need to convince progressive members of their own party of the merits of that strategy. And that could be a difficult task. Some progressive groups view Third Way’s centrist political ambitions as emblematic of the type of establishment politics they believe failed the Democratic Party during the presidential election, and are likely to push back on, or outright reject, whatever the think tank suggests as a result.

But perhaps the most salient challenge for Democrats all across the partisan spectrum will be whether they can accept political reality—whatever that may be—and what it dictates about the future of the political left, even if it contradicts their own vision of what the party should look like.