Hillary Clinton is trying to tar Donald Trump with the sins of the alt-right, a term that has been wildly popular for the last 10 minutes.

But we need to be careful about holding candidates responsible for the views of their supporters, especially those on the fringes of the left as well as the right. That is a dangerous game.

How, for instance, was it Trump’s fault that David Duke decided to endorse him? The media obsessed on how quickly Trump disavowed him, but he can’t be blamed for every wacko that gets behind him.

By the same token, how was it Clinton’s fault that the Orlando killer’s father showed up, uninvited, at one of her events?

It’s a bit different when one of the candidate’s surrogates ventures into dark territory. New Hampshire state rep Al Baldasaro, an adviser to Trump on veterans’ issues, didn’t draw a rebuke for saying Clinton should be shot. But most of the media didn’t think to ask Clinton to apologize for Cher likening Trump to Stalin, Hitler and a child-killer character--at a fundraiser with the former first lady.

Clinton was obviously trying to appeal to moderate Republicans when she painted Trump as the champion for prejudiced groups in a speech the other day:

“He's taking hate groups mainstream and helping a radical fringe take over one of the Republican Party… 

“A man with a long history of racial discrimination, who traffics in dark conspiracy theories drawn from the pages of supermarket tabloids and the far dark reaches of the internet, should never run our government or command our military.”

Trump, of course, responded by calling Clinton a bigot who cares about the votes, but not the lives, of African-Americans.

What gave Clinton an opening was Trump hiring as his campaign CEO the chairman of Breitbart, Steve Bannon, who has described the conservative website as the voice of the alt-right. Breitbart had 18 million visitors last month, putting it ahead of some rival conservative sites.

In her speech, Hillary read some unsavory Breitbart headlines:

"Birth Control Makes Women Unattractive and Crazy." 

"Would You Rather Your Child Had Feminism or Cancer?"

"Gabby Giffords: The Gun Control Movement's Human Shield."

But what, exactly, is the alt-right, which rejects the GOP establishment and the traditionally conservative media?

Here’s the New York Times description

“The alt-right claims to support the preservation of white culture in the United States, and many of its members want to see an overhaul of the entire political system. However, its views are widely seen as white supremacist and anti-Semitic.”

“Widely seen” being journalese for this is what’s really true.

In its lead story on Saturday, the Times quotes Breitbart editor in chief Alexander Marlow as calling Hillary’s assault “a big moment. A major presidential candidate engaging us like that, and calling us out directly, was quite thrilling.”

On the other hand, a Breitbart statement called the Clinton speech “one of the most bizarre, paranoid, conspiratorial presidential campaign speeches in recent memory.”

NBC says alt-right “is derived from ‘AlternativeRight.com,’ a onetime web publication published by Richard Spencer, who, like a number of figures associated with the ‘alt-right,’ belongs to the ‘white nationalist’ movement. White nationalists argue that white Americans must form a united interest group that rejects multiculturalism and blocks immigration in order to keep the country more racially homogenous.”

(And, by the way, one of its top targets is…the all-female remake of “Ghostbusters.” Go figure. A Breitbart editor was banned by Twitter for his messages targeting Leslie Jones, an actress in the film whose website was later hacked and filled with stolen nude photos.)

For another perspective on the alt-right, let’s turn to…Breitbart:

“Some — mostly Establishment types — insist it’s little more than a vehicle for the worst dregs of human society: anti-Semites, white supremacists, and other members of the Stormfront set. They’re wrong…

“Part of this is down to the alt-right’s addiction to provocation. The alt-right is a movement born out of the youthful, subversive, underground edges of the internet. 4chan and 8chan are hubs of alt-right activity. For years, members of these forums – political and non-political – have delighted in attention-grabbing, juvenile pranks.”

But the hiring of Bannon doesn’t mean that Trump embraces every view of every precinct of this amorphous coalition.

The alt-right may be a tempting target for Clinton, but both candidates should be held accountable for their views and their rhetoric, not the attitudes and antics of far-flung supporters.

Howard Kurtz is a Fox News analyst and the host of "MediaBuzz" (Sundays 11 a.m. and 5 p.m. ET). He is the author of five books and is based in Washington. Follow him at @HowardKurtz. Click here for more information on Howard Kurtz.