Chris Christie, the former governor of New Jersey who is challenging Donald J. Trump for the Republican presidential nomination, said Mr. Trump’s rhetoric of intolerance — as evident today as it was during his presidency — had fueled the surge of bigotry confronting Jews and Muslims after Hamas’s brutal Oct. 7 attack on Israel and the fierce Israeli response in Gaza.

And Mr. Trump’s lopsided adherence to the wishes of Israel’s right-wing government, while widely praised in Republican circles, secured only the “low-hanging fruit” of Middle Eastern diplomacy during his presidency, Mr. Christie said, denigrating one of Mr. Trump’s chief foreign policy accomplishments.

He argued that Mr. Trump’s lack of “intellectual curiosity” and foreign policy ambition had led his administration to give up the pursuit of a more elusive peace between Israelis and Palestinians.

Mr. Christie delivered a scathing assessment of Mr. Trump’s Middle East policy in an interview as he traveled to Israel on Sunday for what proved an emotional one-day visit in which he toured a kibbutz, Kfar Azza, near Gaza, where 58 residents were butchered by Hamas terrorists last month. Mr. Christie watched raw footage of the attacks at a military base near Tel Aviv, commiserated with survivors and families in a hospital and conferred with Israel’s president, Isaac Herzog, in Jerusalem.

In the interview, Mr. Christie discussed Israel’s crisis — and the repercussions felt around the world — from the perspective of a man who has known Mr. Trump well for years, advised him and then turned against him.

Mr. Christie’s criticism of the former president’s Middle East record is significant. The peace agreements struck by Israel with the United Arab Emirates, Bahrain, Sudan and Morocco, collectively known as the Abraham Accords, are widely seen as perhaps Mr. Trump’s most important diplomatic accomplishment. And Republicans have offered high praise for decisions like moving the United States Embassy in Israel to Jerusalem from Tel Aviv.

President Biden’s own diplomatic efforts to secure a peace agreement between Israel and Saudi Arabia, which were underway in earnest before the Gaza war broke out, were widely viewed as building on Mr. Trump’s achievements.

Mr. Christie offered higher praise for Mr. Biden’s handling of the Israel-Gaza crisis, including his Oct. 18 visit to Israel, where he met with Prime Minister Benjamin Netanyahu.

He accused Mr. Trump of cynicism in his handling of the once broadly bipartisan U.S.-Israel relationship and held him responsible for fractures over Israel within the Democratic Party.

Mr. Christie said that President Barack Obama’s policies had been perceived as favoring Israel’s enemies and that Mr. Trump had seized the political opening that presented: He wholeheartedly embraced every policy pressed by Israel’s conservative government, including moving the embassy, recognizing Israel’s annexation of the Golan Heights, withdrawing from Mr. Obama’s deal with Iran to temper its nuclear ambitions and pursuing regional peace agreements between Israel and the Persian Gulf states that isolated Palestinians and marginalized their demands for political autonomy.

“I don’t think he has any principles on the issues at all,” Mr. Christie said. “I think it’s just that he saw a public opportunity that Obama presented and he took it.”

Mr. Christie argued that Democratic voters, in turn, had reflexively opposed anything embraced so wholeheartedly by Mr. Trump, including by electing representatives to Congress like Rashida Tlaib of Michigan and Ilhan Omar of Minnesota, whom they saw as fierce opponents of Mr. Trump. Those new lawmakers on the Democratic left then opened an anti-Israel wing of the Democratic Party that is straining the U.S.-Israel alliance.

Meanwhile, he said, the cause of Israeli-Palestinian peace, once considered the holy grail of presidential diplomacy, was all but forgotten.

“I don’t think he was equipped to deal in a foreign policy way with a very difficult, if not impossible, issue, right? And I don’t think he has any ambition,” Mr. Christie said. “I think he was looking for what would be relatively direct and easy scores because his view always was political.”

“If Chris Christie thinks strengthening the U.S.-Israeli alliance, moving the embassy to Jerusalem, bringing peace to the Middle East with the Abraham Accords and enacting laws to protect Jewish Americans is low-hanging fruit, he is clearly living in a fantasy world not rooted in reality,” said Steven Cheung, a spokesman for Mr. Trump’s presidential campaign.

Mr. Christie was quick to say that he did not blame Mr. Trump for the bloody hostilities in Israel. The timing of Hamas’s attack reflected larger geopolitical dynamics with Iran, Russia and China, he said.

But Mr. Christie’s immersion in the horrors of Oct. 7 seemed evident in his changed tone throughout the day.

Before arriving in Israel, he spoke of the difficult balancing act between the vital need for Israel to defend its territory and its people and concerns about the growing backlash around the globe.

“We’ve been there after 9/11,” he said. “We understand the visceral need and the practical need to retaliate and degrade Hamas.”

“But don’t have exclusively a near-term view,” he advised. “And that’s tricky for somebody like Netanyahu and the political position he’s in at the moment, because, you know, there’s certainly going to be a reckoning whenever the war is considered concluded, as to how Israel got there in the first place.”

Mr. Christie later toured one of the kibbutzim hit hard by Hamas terrorists, saw bullet-riddled children’s quarters and spoke to Simcha Greiniman, a volunteer who described one scene in which the charred remains of an entire family clinging to one another — two children, their parents and a grandmother — had to be pried apart.

He watched raw footage, shown at a military base, recovered from cameras worn by Hamas marauders and from the smartphones of victims before their deaths. He remarked not only on the carnage and terror but on the joy expressed by the young terrorists exulting in their deeds.

By day’s end, Mr. Christie, too, was speaking of putting any resumption of a Palestinian peace process “on the back burner.”

“Ultimately, it’s in Israel’s best interest and the world’s best interest. But I think the actions that Hamas took on Oct. 7 has made that resolution significantly more difficult and more long-term. And I think that’s one of the real shames of their actions,” he said on Sunday night.

In the interview, before arriving in Israel, Mr. Christie traced the surge in public expressions of anti-Jewish and anti-Muslim bias since the war began in part back to Mr. Trump’s often inflammatory rhetoric.

“I don’t think Trump’s an antisemite,” even though he has routinely espoused stereotypes of Jews, Mr. Christie said. But, he added, Mr. Trump’s “intolerance of everybody” is “what’s contributed to” the surging bigotry.

“He says what he says, without regard to the fact that he’s perceived as a leader and that his words matter,” Mr. Christie said. The bigots “think you’re giving them permission be a bigot,” he added, “and that’s even worse than them thinking you are one.”

Mr. Trump has bristled at accusations that he is antisemitic, pointing to his daughter Ivanka, a Jewish convert, and her Jewish children.

Mr. Christie put little stock in that.

“That’s just him looking at a convenient out that he thinks ends the conversation. He doesn’t want to have the conversation,” he said of Mr. Trump’s protest that he has Jewish grandchildren. “I don’t buy that at all in terms of a proof point on anything.”

Mr. Trump’s well-chronicled habit of trotting out Jewish stereotypes — saying he only wanted “short guys that wear yarmulkes” counting his money, calling Jewish real estate executives “killers” and telling those at a gathering of the Republican Jewish Coalition that they were all tough deal makers — is of a piece with stereotypes he holds for Italian Americans, Black Americans and Muslim Americans, Mr. Christie said dismissively.

“I think he’s a guy of the 1960s from Queens, New York, with certain attitudes that he probably learned from his parents,” Mr. Christie said.

But he was less sympathetic about the bigotries that he said Mr. Trump had unleashed.

“His rhetoric contributes to it,” he said. “By his rhetoric, I mean, his intolerance of everybody. Everybody hears that dog whistle a different way.”