Sen. Bernie Sanders (I-Vt.) has never attended an American Israel Public Affairs Committee conference, according to the lobbying group. In fact, his public refusal to attend last year’s conference early in his bid for the 2020 Democratic nomination spurred a petition that urged other presidential candidates to steer clear of the pro-Israel lobbying group’s event.

Things have changed since last year, but the senator from Vermont on Sunday again denounced the conference, which he called a platform for “leaders who express bigotry and oppose basic Palestinian rights.” In doing so, Sanders has reignited the debate over the lobby’s influence in U.S. politics, at a time when some detractors have compared his supporters and campaign victories to the rise of the Nazis.

In response, AIPAC, which calls itself a “pro-Israel lobby” and holds substantial sway in foreign policy debates involving Israel and the Palestinian territories, described Sanders’s position on Sunday as “truly shameful.”

“Sen. Sanders has never attended our conference and that is evident from his outrageous comment,” AIPAC said in a tweet Sunday. “By engaging in such an odious attack on this mainstream, bipartisan American political event, Sen. Sanders is insulting his very own colleagues and the millions of Americans who stand with Israel.”

Sanders’s vow to skip the AIPAC conference, which he made on Twitter on Sunday evening, came the day after he secured a landslide victory in the Nevada caucuses, clarifying a possible path to the Democratic nomination. Sanders dominated headlines over the weekend, and a “60 Minutes” interview Sunday night in which he defended past statements made about aspects of Fidel Castro’s rule over Cuba trended into early Monday.

Sunday’s Sanders-heavy news cycle offered a window into how the senator will navigate the next stretch of his campaign, after seizing a commanding position in the primary race.

The fact that arguably the most left-leaning candidate in a crowded field of Democratic challengers secured an early lead has shocked many observers. Among those is MSNBC “Hardball” host Chris Matthews, who was so struck by the candidate’s success Saturday that he compared Sanders's victory in Nevada to Nazi Germany’s invasion of France in 1940.

“It looks like Bernie Sanders is hard to beat right now,” Matthews said. He continued discussing Saturday’s Nevada caucus results, emphasizing how difficult it may be for another candidate to surpass Sanders, even though he is a party outsider and has been the target of attacks from the Democratic establishment.

“I was reading last night about the fall of France in the summer of 1940, and the general, Reynaud, calls up Churchill and says ‘It’s over,’" Matthews said, comparing the senator’s win to that moment. “And Churchill says: ‘How can it be? You’ve got the largest Army in Europe, how can it be over?’ He said, ‘It’s over.’”

Matthews’s comment drew harsh criticism from Sanders supporters who viewed it as unfair and insensitive because Sanders is Jewish.

Progressive Jewish advocacy group IfNotNow slammed Matthews and MSNBC on Twitter for using “Nazi comparisons when talking about @BernieSanders, a Jewish candidate with family that was murdered in the Holocaust.”

An MSNBC contributor raised the issue on “AM Joy” Sunday morning.

“Why is Chris Matthews on this air talking about the victory of Bernie Sanders, who had kin murdered in the Holocaust, analogizing it to the Nazi conquest of France?” said Anand Giridharadas, an editor-at-large for Time magazine, during the MSNBC program. “It is time for all of us to step up, rethink the dawn of what may be, frankly, a new era in American life.”

MSNBC did not immediately return a request for comment late Sunday.

Critics also pointed to an instance earlier this month in which MSNBC anchor Chuck Todd cited a conservative column that called Sanders supporters “brown shirts” on-air while discussing online harassment by so-called Bernie Bros. The cable network was panned online for implying that his fans have a Nazi-like fanaticism and using an analogy that casts Sanders, whose Polish relatives were murdered in the Holocaust, as a Hitler-like figure.

“'Digital brown shirt brigade.’ That’s how our Jewish candidate’s supporters are being described on the MSM,” Sanders campaign national press secretary Briahna Joy Gray tweeted after the segment aired this month. “The contempt shown for ordinary people is really something.”

Sanders's Jewish identity came to the forefront again Sunday evening when he announced his intent to miss the AIPAC conference. Top Democratic leaders, including House Speaker Nancy Pelosi (D-Calif.) and Senate Minority Leader Charles E. Schumer (D-N.Y.), were speakers at last year’s conference. Senate Majority Leader Mitch McConnell (R-Ky.) and House Majority Leader Steny H. Hoyer (D-Md.) are slated to speak at next month’s event.

It’s unclear whether other Democratic candidates will opt to skip AIPAC this year. At least 12 high-profile Democrats, all of whom were likely 2020 presidential candidates at the time, opted out in 2019. Several of Sanders’s current Democratic challengers, including Sens. Elizabeth Warren (Mass.) and Amy Klobuchar (Minn.) and former South Bend, Ind., mayor Pete Buttigieg, did not show up in 2019.