Thousands of protesters gathered outside Trump Tower the day after he won the presidential election, Nov. 9, 2016. View Full Caption DNAinfo/Ben Fractenberg

NEW YORK CITY — The same post-election atmosphere that's spurred right-wing extremists and hate crimes could also spark a wave of left-wing violence, anti-hate advocates fear.

The Tuesday election of Donald Trump to the presidency sparked a wave of nationwide protests and smaller-scale clashes, which has the director of the Anti-Defamation League's Center on Extremism worried about the rise of hate across the ideological spectrum.

"It's very possible with this election, and how divisive it’s been, that we may see left-wing extremism make a come back. I hope not," said the center's director, Oren Segal.

While Segal has yet to see any large-scale organized efforts like the Weather Underground of the 1960s in which self-described leftist revolutionaries plotting to overthrow the United States government blew up several buildings including a townhouse on West 11th Street, he's noticed smaller worrisome signs.

A man was choked aboard a 5 train in Union Square for wearing a baseball cap with Trump's slogan, "make America great again" on Tuesday, police said.

A similar incident occurred in Chicago.

Rioters in Oregon and California angry about Trump's victory broke storefront windows, hurled Molotov cocktails and vandalized buildings, according to reports. Protesters here in NYC wrote "f--k Trump" on an NYPD car and stomped on its hood.

The Southern Poverty Law Center, which tracks hate groups and incidents across the country, has collected 20 reports of anti-Trump intimidation and harassment from the day the candidate claimed victory through Nov. 14. Staff at the Law Center haven't followed up on user-submitted reports, they said.

Segal's already heard protesters chant things like "assassinate Trump" in New York and "rape Melania" elsewhere, both chants he strongly condemns.

This is disgusting and should be added to any list of post-election hate incidents. #ExposeHate #Melania #Trump https://t.co/lHqBKqDPj2 — Oren Segal (@orensegal) November 15, 2016

"That’s unacceptable whether its New York City or anywhere else. I hope as people are using this moment to express frustration and concerns that we don’t stoop the level of those on the fringes who’ve been emboldened by this presidential campaign," Segal said.

"Fighting hatred and bigotry with more militancy and bigotry at times like this is not going to solve the problem," he added.

Trump's victory also seems to have emboldened racist bigotry nationwide, according to the Southern Poverty Law Center, which has collected 437 reports of harassment and intimidation nationwide (including the 20 anti-Trump incidents).

New York hasn't been immune, with 26 incidents, the Law Center reported.

The city may also appear to be a safe haven, but Segal said its vast population and the large Jewish community can draw a surprisingly large number of hate crimes.

In the week since Trump won, a man punched a woman in the face inside a Boerum Hill restaurant because she criticized the president-elect, witnesses said.

Manhattan State-senator Brad Hoylman found a swastika scrawled in his apartment building on Tuesday, he said.

Swastika found in my apartment building this evening in Greenwich Village. Anti-Semite named to #Trump White House post. Connect the dots. pic.twitter.com/3OlD8hewyF — Senator Brad Hoylman (@bradhoylman) November 16, 2016

Vandals have also scrawled swastikas in a predominantly Jewish are of Crown Heights and on the doors of four dorm rooms at The New School.

New York's five district attorney's pledged Tuesday to vigorously prosecute hate crimes in the city.

"Within the past week, our offices have become aware of multiple incidents where New Yorkers received threatening messages relating to their race or religion and we are carefully monitoring these reports," they said in a joint press release.

While the Law Center found there are up to 27 such groups that located within the five boroughs, Segal said these types of incidents tend not to be the work of organized hate groups, but rather one-off acts by individuals.

"Most white supremacists and anti-government extremists don't belong to any organized group at all. They're borrowing from various groups and ideologies to create their worldview," Segal said.

He added that some people have seemingly been newly motivated to act in violent ways by ideas they may have encountered online or popular culture.

"Now, the concern is them feeling emboldened. Are they going to try to engage in activity they normally wouldn’t? Are they going to try to mainstream themselves too? Are they going to engage in violence because they feel emboldened?" he added.

Still, Segal doesn't expect major hate groups like the Ku Klux Klan to make a major appearance in the city.

"New York City isn't the best place for a klansman or a white supremacist. They're not going to feel at home here," Segal said.