Before Hamas attack, US attitudes on Israel and Palestinians had shifted along party lines: Polling

Hamas' militants launched a brutal, expansive terror attack on Israel over the weekend, killing at least 1,200 people, and Israel went to war in response, with President Joe Biden and other top administration officials pledging aid to the Israelis.

That underlines the U.S.'s continued support for Israel. Gallup polling in recent decades shows that adults broadly remain very or mostly favorable to Israel compared with the Palestinian Authority, one of the Palestinians' major governing bodies.

Still, according to Gallup surveys as recently as February -- months before the Hamas attack -- Americans' opinions had been shifting on Israel and the Palestinians, with thoughts on the two largely divided along party lines.

Americans overall also remain supportive of Israel, with 54% in the February Gallup survey saying their sympathies lay more with Israelis, while 31% said their sympathies lay more with the Palestinians.

A special edition of "20/20" at 10 p.m., Wed., Oct. 11, on ABC looks at life under threat in Israel and Gaza and how this attack is different from what we've seen in this region in the past.

Support for Israel in Gallup's polls, all well before Hamas struck, has remained relatively constant since 2001, while support for Palestinians had risen from 16% in 2001.

The percentage of Americans who said their sympathies were with both Israelis and Palestinians or were unsure dropped from 33% in 2001 to 15% earlier this year.

Much of the movement appeared to be driven by Democrats: In 2001, 51% of Democrats told Gallup their sympathies lay more with Israelis, while 16% said their sympathies were more with Palestinians. Those numbers flipped by 2023, with 38% of Democrats saying their sympathies were more with Israelis and 49% saying their sympathies lay more with Palestinians.

January of this year also marked the first time since at least 2001 that more Democrats said their sympathies lay more with Palestinians than with Israelis, 49-38%. Still, 56% of Democrats in March said they had a very or mostly favorable view of Israel.

Republicans, meanwhile, expanded their support for Israel. Fifty-nine percent of Republicans in 2001 said their sympathies lay more with Israelis, and 14% said their sympathies lay more with Palestinians. The percentage of Republicans whose sympathies were more with Israelis jumped to 78% by 2023, with the percentage of Republicans whose sympathies were more with Palestinians falling slightly, to 11%.

Eighty-two percent of Republicans in March said they had a very or mostly favorable view of Israel.

Independents largely split the difference. Forty-four percent in 2001 told Gallup their sympathies lay more with Israelis, and 19% said their sympathies lay more with Palestinians. Two decades later, in 2023, 49% of independents said their sympathies lay more with Israelis, while 32% said their sympathies lied more with Palestinians.

Sixty-seven percent of independents in March said they had a very or mostly favorable view of Israel.

Experts told ABC News that there are several possible explanations for the public opinion shift, though it's unclear if the trend will continue after Hamas' assault on Israel over the weekend.

Since the conflict began, in addition to the dead and wounded in Israel, Palestinian officials said that more than 1,000 people have been killed in Gaza, the Palestinian territory that Hamas controls.

Khaled Elgindy, a senior fellow at the Middle East Institute and a former adviser to the Palestinian leadership in Ramallah on permanent status negotiations with Israel from 2004 to 2009, believes Democrats' drop in support for Israel is due in part to increased awareness of Palestinians' often dire living conditions in the West Bank, which is occupied by Israel, and the Gaza Strip.

Elgindy also pointed to the disproportionate casualty rates between Israelis and Palestinians in past rounds of fighting -- a pattern so far sharply reversed in the latest Hamas terror attack.

Partisanship is another factor driving Democrats shifting sympathies, Elgindy said: "Israeli Politics have shifted ever more to the right over the years."

He said that Israel's national government before the Hamas attack had embraced "more aggressive policies toward Palestinians" and "more settlements" for Israelis in Palestinian territory, which is considered illegal by the U.N.

Before the Hamas attack, such settlements had also been criticized by Biden administration officials.

Experts also suggested that Democrats' shift in opinion was linked to a major domestic issue since 2020 -- the nationwide protests and debate over racial inequality, fueled by movements like Black Lives Matter -- and how that could have reshaped attitudes more broadly.

Still, "being against Israeli policies does not mean to be against Israel per se," Raffaella A. Del Sarto, an associate professor of Middle East studies at the Johns Hopkins University School of Advanced International Studies, told ABC News in an email.

Republicans have grown increasingly supportive of Israel in part, one of the experts said, because evangelicals have become more influential within the party in the U.S. At the same time, fewer Democrats identify as affiliated with an organized religion.

Former President Donald Trump, among the most popular figures in the GOP, sought to define his foreign policy record while in office through his close alliance with Israel's national government.

"Evangelical Christians are a big bloc within the Republican Party base. And they're quite supportive of Israel for theological and religious reasons," Elgindy said, adding, "I think there's a secular version of that trend."