The controversy that swirled around Congress this week after Rep. Ilhan Omar insinuated that politicians only support Israel because of donations from wealthy Jews died down as quickly as it began. Publicly rebuked by leaders of her own party for using “anti-Semitic tropes,” the freshman Democrat issued an apology.

But while this episode was short, the already tricky politics of Israel are likely to keep coming up — and keep getting trickier for Democrats.

As the Democratic Party gears up for a contentious 2020 primary, many observers are warning that the grassroots of the party may not be in sync with the traditionally strong support of Israel among lawmakers of both parties. Changing attitudes among younger voters, Israel’s recent political history and President Donald Trump’s vocal support for the country have all contributed to a shift in public opinion.

“We shouldn’t overlook the fact that on a retail level there is an erosion of support for Israel among Democrats,” said former Rep. Steve Israel, who served in Congress for nearly two decades and also chaired the Democratic Congressional Campaign Committee. “Those of us who support Israel need to educate potential candidates that this is not a political issue; this is not a partisan issue; this is an issue about two democracies in a challenging world.”

Until recently, criticism of Israel was largely relegated to the fringes of both parties. But over the last decade, Israel’s government, led by current Prime Minister Benjamin Netanyahu, has shifted increasingly rightward. The country has defied international pressure by building controversial settlements in the West Bank and passed a measure affirming that the country is a Jewish nation-state, which some Arab Israelis criticized as a move toward a form of apartheid.

As a result, grassroots Democrats have been more open in critiquing what they consider Israel’s human rights abuses against Palestinians and unethical occupation of the West Bank. Polling shows that partisanship on this issue has intensified. The number of Republicans who favor Israel over Palestine in the conflict has increased 29% since 2001, while the number of Democrats who favor Israel has decreased 11% in the same time period, according to a 2018 report from the Pew Research Center.

Dov Waxman, a political science professor at Northeastern University and author of “Trouble in the Tribe: The American Jewish Conflict over Israel,” largely attributes this shift to a growing segment of younger Democratic voters, both Jewish and non-Jewish, who are unafraid to challenge this longstanding bipartisan area of agreement.