For years, Democrats have warned that Prime Minister Benjamin Netanyahu of Israel, with his right-wing politics and policies, was undermining their party’s backing for Israel that dates to the nation’s inception in 1948.

In recent days, amid mounting scenes of starvation and devastation in Gaza, it has become clearer than ever that the longtime bipartisan consensus in support for Israel is, at least for the moment, in tatters.

Democrats have long objected to Mr. Netanyahu’s policies, in particular his efforts to prevent the establishment of a Palestinian state, and his far-right government’s conduct of the Gaza war. But some supporters of Israel fear that the hatred of the prime minister — Israel’s longest-serving leader, who has been in power with only one interruption since 2009 — is metastasizing into a broader rejection of Israel.

Support for Israel’s military action in Gaza has plunged into the single digits among Democrats. Across the country, local Democratic officials are pushing for embargoes on military and financial support of Israel. And long-boiling anger over the Gaza war among the party’s activists is manifesting in striking new ways in the halls of Congress.

On Wednesday night, a majority of the Senate Democratic caucus, including more moderate lawmakers, voted for a resolution calling to block the export of automatic assault rifles for use by the Israel National Police, which is overseen by Itamar Ben-Gvir, perhaps the most extreme right-wing member of the government.

A slightly smaller group voted for a measure urging the blocking of the sale of some bombs.

The measures failed, but they amounted to an extraordinary rebuke of the Netanyahu government and its handling of the escalating humanitarian disaster in Gaza.