Senate Majority Leader Chuck Schumer's (D-N.Y.) speech calling for a new government in Israel landed like an earthquake Thursday, delivering a huge shock to the already tense U.S.-Israel relationship.

Why it matters: In addition to being the most senior Jewish elected official in the country, Schumer has had one of the longest and closest relationships with Israeli Prime Minister Benjamin Netanyahu of any U.S. politician.

• Schumer's speech stunned officials and observers in both Washington and Jerusalem because he has been — and still is — the Democratic Party's most avid supporter of Israel in decades.
• His harsh remarks about Netanyahu create more political space for other Democratic members of Congress to publicly voice their criticism of the Israeli government amid the ongoing war in Gaza.

Flashback: To understand how significant the comments were, one must return to March 2015 — when Schumer was one of the only Senate Democrats who didn't criticize Netanyahu's famous speech to Congress railing against the Iran nuclear deal.

• Several months later, Schumer was one of the only Senate Democrats to vote against the deal — defying President Obama and siding with Netanyahu.
• This is why Schumer was the last person Netanyahu expected to stand on the Senate floor Thursday and call him one of "four major obstacles to peace" — along with Hamas, Palestinian Authority President Mahmoud Abbas and radical right-wing Israelis.

Between the lines: U.S. officials and Senate Democrats say Schumer's comments reflect the change in public sentiment toward Netanyahu's government — especially inside the Democratic Party and the mostly liberal Jewish American community.

• One Democratic senator said that in 2015, Schumer wouldn't have been able to set foot in many New York synagogues if he voted in favor of the Iran deal; after this speech, he'll be welcomed there with praise.
• The senator added that Schumer's speech reflects what the majority of Jews in America feel — they support Israel and want to destroy Hamas, but are fed up with Netanyahu and his radical right-wing government.

Behind the scenes: Schumer told senior White House officials on Wednesday that he was going to give a speech about Israel, but he didn't give them a copy of the speech or ask for their permission, U.S. officials told Axios.

• The White House didn't encourage Schumer, but also didn't stop him. Several White House officials were surprised by how harsh he was.
• "I don't know if people in Israel really understand how big of a step it is for him to do this," one U.S. official said.

The big picture: The White House has sought to tamp down its public spat with Netanyahu in recent days, after concluding that the escalating tensions only serve the Israeli prime minister's domestic political interests, a U.S. official said.

The intrigue: This was the second time this week that a U.S. official publicly commented on Netanyahu's political weakness.

• On Tuesday, the director of national intelligence's annual threat assessment determined that Netanyahu's "viability" as prime minister may be in jeopardy due to Israeli discontent.

How it's playing: Netanyahu, who over the years has been accused many times of meddling in U.S. politics, hit back hard against Schumer's comments.

• "Israel is not a banana republic but an independent and proud democracy that elected Prime Minister Netanyahu," the ruling Likud Party said in a statement, accusing Schumer of undermining a democratically elected government.
• Polls published Wednesday in all three major TV channels in Israel found that the majority of Israelis want early elections — and that if elections were held today, Netanyahu would be defeated by his rival minister Benny Gantz.
• But Gantz chose to distance himself from Schumer's comments, saying that the Senate leader made a mistake by giving such a speech and that any intervention in Israel's domestic politics is unacceptable.

Go deeper: Schumer sparks Democratic discord with Netanyahu speech