Democrats hoping for a united front against President Donald Trump in 2020 are trying to avoid splintering over an increasingly thorny topic: the Israeli-Palestinian conflict.

With an energized progressive base increasingly supportive of Palestinian rights, and a president who is stridently pro-Israel in his policy moves, Democrats are starting to grapple more than ever with the party’s once-reflexive support for Israel.

The 2020 Democratic presidential contenders are saying little publicly as they balance the competing interests. But in the meantime, pro-Israel Democrats are scrambling behind the scenes to shore up support, providing Holy Land trips to members of Congress and proposing policies they hope can bridge a growing party divide.

Against this backdrop, Democratic Rep. Ilhan Omar of Minnesota — one of the first two Muslim women ever elected to Congress — apologized on Monday for what many regarded as anti-Semitic criticisms she leveled on Twitter.