Speaker Mike Johnson (R-La.) and Senate Minority Leader Mitch McConnell (R-Ky.) sent a letter to President Biden expressing alarm about the White House decision to put on hold a weapons shipment to Israel and asking for details about the decision by the end of the week.

Why it matters: The unprecedented move by the Biden administration, first reported by Axios on Sunday, was a way for the U.S. to signal its concern over Israel's plans for a possible ground invasion of Rafah, U.S. officials said.

• The weapons shipment to Israel included 1,800 2,000-pound bombs and 1,700 500-pound bombs, a senior U.S. official said.

State of play: More than 1 million displaced Palestinians have been sheltering in Rafah, a city in the southern Gaza Strip that Israel says is Hamas' last military stronghold.

• The Biden administration is opposed to any major ground operation Israel conducts in Rafah that doesn't include a credible plan for protecting civilians.
• On Monday, Israel captured the Palestinian side of the Rafah crossing on the eastern outskirts of the city.
• The White House sees the Rafah operation as "limited" so far and doesn't believe Israel has crossed President Biden's "red line," which could lead to a shift in U.S. policy toward the war in Gaza, U.S. officials told Axios.
• But the officials warned that if the operation broadens or gets out of control — and Israeli forces go into the city of Rafah itself — it will be "a breaking point" for U.S.-Israeli relations.

What they're saying: "This news flies in the face of assurances provided regarding the timely delivery of security assistance to Israel," Johnson and McConnell wrote Biden, referring to the decision to pause the weapons shipment to Israel.

• They added that they believe security assistance to Israel "is an urgent priority that must not be delayed."
• Johnson and McConnell wrote that the decision to stop the weapons shipment calls "into question your pledge that your commitment to Israel's security will remain ironclad."

Behind the scenes: In the letter, Johnson and McConnell claim that only after the White House decision was published in the press and their staff inquired about it did they learn from the president's staff that "a review of a specific weapons shipment" was underway.

• "The American public deserves to understand the nature, timing, and scope of these reviews," they wrote.
• They added that "daylight between the United States and Israel at this dangerous time risks emboldening Israel's enemies and undermining the trust that other allies and partners have in the United States."

Zoom in: Several pro-Israel Democrats told Axios they are still trying to pry information from the administration about their reasoning behind the pauses.

• "I have asked for a confidential briefing. I would like to know why they made that decision," Rep. Kathy Manning (D-N.C.) told Axios, declining to take a firm position on the move until she knows more.
• Another House Democrat told Axios they "don't get the sense it's a big deal yet" and said Republicans are seizing on it as a "political opportunity" to bash Biden.

Rep. Brad Sherman (D-Calif.) and Rep. Jared Moskowitz (D-Fla.) both said their understanding of the administration's pause is that it is meant to send a message to Israel about minimizing civilian casualties.

• "I see it as an act of communication … they want Israel to get Hamas, just don't do anything [Hamas] would have done," Sherman said.
• "Obviously this [is] messaging," Moskowitz said.

Sen. John Fetterman (D-Pa.) told Axios he "strenuously disagrees" with Biden's decision. The staunchly pro-Israel senator said the delay of the weapons "empowers Hamas to continue to deny accepting peace."

But most other Senate Democrats fell in line behind Biden's decision, arguing the U.S. should use their leverage to make sure operations in Rafah do not cost civilian lives.

• "I think if [Israeli leaders] don't demonstrate that they're going to come up with a better plan, I think it's a reasonable thing to consider how we are going to condition aid," Sen. Mark Kelly (D-Ariz.) told Axios.
• Sen. Tim Kaine (D-Va.) told Axios that he was "gratified" when Biden decided to pause the shipment. "Weapons that are likely to lead to more civilian casualties, it's time to pause those," Kaine said.

What's next: Johnson and McConnell ask Biden to provide "relevant responses" by the end of the week on the timing of the review of the weapons shipment, whether any other shipments are reviewed or paused, and when the review is anticipated to end.