WASHINGTON (AP) — Joe Biden had been to Dachau, the infamous concentration camp in Germany, several times before, but he sensed changes when he visited as vice president with a teenaged granddaughter.

“It seemed as though things had been rearranged to make visitors less uncomfortable,” he recalled in a memoir published two years after the 2015 visit. “They had softened the cruel edges over the years.”

Unwilling to settle for what he believed was a more sanitized experience, Biden asked the guides to bring them to the gas chamber, where they “slammed the door behind us with a frightening clank.”

For Biden, it’s a direct line from there to the Hamas attacks on Israel, which caused the largest loss of Jewish life in a single day since the Holocaust.In a searing speech from the White House, Biden said the bloodshed “brought to the surface painful memories and the scars left by a millennia of antisemitism and genocide of the Jewish people.”

The massacres and kidnappings have sparked a crisis that threatens to engulf more of the Middle East. They’ve also resonated deeply for the U.S. president, whose devotion to Israel is rooted in a childhood that saw the birth of the Jewish state and in a political career that parallels repeated threats to destroy it.

Biden’s support has remained solid over the years even as some corners of his Democratic Party have urged a more critical approach to Israel and its decades-long occupation of Palestinian territory, which is widely viewed as illegal by the international community.

“He’s a politician of a generation that probably doesn’t exist anymore,” said Aaron David Miller, who has advised both Democratic and Republican administrations on the Middle East.

Biden’s commitment could be tested if Israel launches an incursion into Gaza, where Hamas is headquartered, in a military operation that would compound the suffering already experienced by Palestinians facing waves of retaliatory bombardment.

For now, Biden has offered only vague admonitions that Israel should follow the rules of war, which United Nations officials say are being violated by its siege tactics leading to dwindling supplies of food, medicine and electricity.

Instead, Biden’s focus has been on demonstrating “unshakable” solidarity with Israel, including his remarks during a White House meeting Wednesday with Jewish leaders to talk about combating antisemitism.

“Were there no Israel, no Jew in the world would be ultimately safe,” Biden said. “It’s the only ultimate guarantee.”

During Biden’s remarks, he recalled his visits to Dachau, saying some doubted whether it was appropriate to bring his grandchildren, and his children before them, to the concentration camp when they were young. It was important, he said, to demonstrate not only the cruelty of the Holocaust but the apathy that allowed it to take place.

“I wanted them to see,” Biden said, his voice rising, his fist rapping on the lectern, “that you could not not know what was going on.”

Amy Spitalnick, a leader of the Jewish Council for Public Affairs who attended the Wednesday meeting, said it’s clear that Biden “feels it in his kishkes, as my grandmother would have said,” using a Yiddish word for gut.

“There was deep appreciation for the moral clarity that the president has had,” she said.

It’s a lesson that Biden traces to his father, who he describes as having a “preoccupation with the Holocaust.” Biden was born in 1942, three years before the end of World War II and six years before Israel’s founding, coming of age at a time when the world was reckoning with genocide.

At the dinner table, then-senator Biden recalled during a 1999 hearing on antisemitism in Russia, his father would often talk about “how the world stood silently by in the 1930s in the face of Hitler.” Biden added that he is “a Zionist in my heart.”

Biden has met every Israeli prime minister over more than five decades in elected office, starting with Golda Meir in 1973. It’s a story he frequently retells, most recently on Tuesday.

During Biden’s first trip to the country after being elected senator, he said Meir sensed his concern about the country’s future. As they were posing for a photo after their meeting, Biden recalled, she whispered to him that Israel had a “secret weapon” to protect them — “we have no place else to go.”

It was a remark that encapsulated Israel’s back-against-the-wall perspective as a new nation surrounded by hostile Arab countries, some of which would invade only weeks later in the Yom Kippur War.

But Biden also recognized another challenge, according to a classified Israeli document describing the meeting and obtained by Israel’s Channel 13 in 2020. He told Meir that Israel should begin relinquishing Palestinian territory that had been seized during the Six-Day War of 1967.

Much of that land remains under Israeli control, and Biden acknowledged last year during a visit to Bethlehem, in the occupied West Bank, that there was little immediate hope of advancing the peace process.

Biden also stopped in Jerusalem during the trip, and his remarks there were a window into how he has tried to balance Israel’s imperiled beginnings and its current status as a regional power.

He noted that his first stop after arriving in Israel was Yad Vashem, the Holocaust memorial, so he could “renew our vow of never again.”

However, he said, “the Israel of today is not the Israel of 50 years ago,” with “new tools that keep Israel strong and secure,” not to mention “an ironclad commitment from the United States of America to Israel’s security.”

Over the years, Biden has projected public support for Israel while also expressing private concerns about some of its actions.

Frank Jannuzi, who worked for Biden when he was chair of the Senate Foreign Relations Committee, remembered how the senator gave explicit guidance that any disagreements with Israel should be handled quietly.

“It was very important in public venues, whether that is before Congress or the media or on the international stage, for the United States to stand shoulder to shoulder with Israel,” Jannuzi recalled.

Biden’s reason, Jannuzi said, was that “if Israel felt insecure in the world, or isolated, because America had somehow distanced itself, then Israel would be less likely to listen to our advice.”

Biden has made rare departures from that approach when dealing with Israeli Prime Minister Benjamin Netanyahu, who leads a right-wing coalition government that includes ultranationalist leaders.

Netanyahu is pushing changes to his country’s judicial system in a way that critics say would erode its democracy, and earlier this year Biden said the Israeli leader “cannot continue down this road.”

The issue resurfaced when the two leaders met last month.

“We’re going to discuss some of the hard issues, that is upholding democratic values that lie at the heart of our partnership, including the checks and balances in our systems,” Biden said at the time.

The disagreements have not precluded Biden and Netanyahu from working together toward establishing diplomatic relations between Israel and Saudi Arabia, an effort that could be derailed by the latest fighting.

And since the Hamas attacks on Saturday, Biden and Netanyahu have spoken repeatedly, most recently on Wednesday. Israeli officials and commentators across the political spectrum have expressed gratitude for Biden’s backing, undercutting Republican criticism of the White House’s approach to the region.

The U.S. president “just set a new standard of support for the Jewish state and the Jewish people in times of tragedy and war,” Herb Keinon wrote in the Jerusalem Post.

The U.S. has begun shipping munitions and military hardware to Israel, and an aircraft carrier strike group was deployed in the Eastern Mediterranean in a show of force intended to deter a wider conflict. Secretary of State Antony Blinken arrived in Tel Aviv on Thursday.

“We will make sure the Jewish and democratic State of Israel can defend itself today, tomorrow, as we always have,” Biden said on Tuesday. “It’s as simple as that.”

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Associated Press writer Amy Teibel contributed from Jerusalem.