(CNN) - There are few issues as contentious in international politics as the Israeli-Palestinian conflict.
But for the better part of the past two decades, the establishment wings of both the Republican and Democratic Party have largely been pro-Israel. Both parties have, at least in their party platforms, maintained pro-Israel positions, including calls to recognize Jerusalem as the Jewish nation's capital.
While the Republican Party has become more pro-Israel recently, it's unclear whether the Democratic Party will be able to maintain a pro-Israel tilt.
Today, the Pew Research Center finds Democrats are less pro-Israel than they've been in decades. That drop has occurred in a period of just two years since 2016.
This year, 27% of Democrats said their sympathies lied with the Israel over the Palestinians in their conflict, while 25% said the Palestinians. The rest said both or neither. Just two years ago (when the Democrats adopted more pro-Palestinian positions in their plank), 43% of Democrats said their sympathies aligned with Israel compared with 29% who said the Palestinians.
It's not just that Democrats are split, it's how they're split. Establishment Democrats have been fighting off an insurgent progressive wing, and it's not any different on this issue. Liberal Democrats who pushed for the more pro-Palestinian language are far more likely to side with the Palestinians than the Israelis (by a 35% to 19% margin). Meanwhile, moderate and conservative Democrats still go with Israel (by an inverse 35% to 17% margin).
There's also an age gap on the issue that has dominated Democratic divisions dating back to the 2016 primary. In 2016, those under the age of 30 who called themselves Democrats or independents who leaned towards the Democratic Party said by a 39% to 31% margin that their sympathies aligned with the Palestinians rather than the Israelis. Among those Democrats age 65 years and older, the split was 50% for Israel compared to 24% for the Palestinians.
Indeed, while there are many issues that parade themselves as ones that fall along the Hillary Clinton vs. Sanders divide in the party, the Israeli-Palestinian conflict definitively does. Back in 2016, Clinton supporters were by a 20-point margin more likely to have their sympathies towards the Israelis than the Palestinians, while Sanders supporters backed the Palestinians over the Israelis by a 6 point margin, according to Pew.
Over the last two cycles, Israel has become a divisive issue in the Democratic Party platform. Only at President Barack Obama's insistence in 2012 was Jerusalem recognized as the capital of Israel. Even with his backing, there was a contentious floor voice vote.
In 2016, more pro-Palestinian language was put into the platform. It called for a Palestinian state with "independence, sovereignty, and dignity." A plank calling for "an end to occupation and illegal settlements" sponsored by Bernie Sanders' supporters was barely defeated in committee
It's not too difficult to imagine the Democratic Party will move towards the Palestinian position over the next few years. It's not just that liberal Democrats (who are the least pro-Israel) are becoming a larger share of the Democratic electorate. It's that there could be a negative backlash to Trump's designating Jerusalem the capital of Israel and the violence that escalated in the aftermath. Just 14% of Democrats said we should have moved the embassy in a December 2017 CNN poll.
How exactly the rift will play out in the 2020 platform discussions and the 2020 Democratic primary field isn't clear. It does seem, however, that there will be more discussion of the issue leading up to and during the primary than in recent history.