The ad you knew was coming has arrived.

An ad released by the Hillary Clinton campaign says white supremacist and alt right leaders support Donald Trump for president. (Hillary Clinton)

The spot was released a few hours before a planned Hillary Clinton speech tying Donald Trump to the "alt-right," a nebulous term usually used to describe a group of online pro-Trump trolls who have often used racist or anti-Semitic images to show their support. The alt-right is actually a bit more complicated than that, but the racist wheel gets the media attention, as the old saying goes.

Recognizing that most people have no idea what the alt-right is, Clinton's ad instead focuses on a much more immediately offensive group: the Klan. There's no Ku Klux Klan endorsement process (though there used to be) so Clinton relies a bit of guilt-by-association, looping in comments from a famous former Klansman (David Duke) and an anonymous current one, interviewed while in full robe and hood.

The alt-right link is nebulous in a different way. While Trump's new campaign CEO, Steve Bannon, once boasted that his Breitbart News site was "the platform for the alt-right," Bannon denies that he's embracing the racist side of the movement. He told Mother Jones's Sarah Posner that he saw the site as nationalist — but not a nationalism focused on racial identity. As he put it to Posner: "Look, are there some people that are white nationalists that are attracted to some of the philosophies of the alt-right? Maybe. Are there some people that are anti-Semitic that are attracted? Maybe. Right? Maybe some people are attracted to the alt-right that are homophobes, right? But that's just like, there are certain elements of the progressive left and the hard left that attract certain elements."

All of this, though, is meant to continue to put pressure on a weakness for Trump: the perception that he himself is bigoted or racist. The Post reported this week on his campaign's efforts to push back against that notion. It's a perception so strong that a fifth of Republican men and a quarter of Republican women said in a recent Washington Post-ABC News poll that they thought Trump harbored some bias against women or minorities. More than 50 percent of voters overall felt that he did, including nearly three-quarters of nonwhites.

It's hard to say how directly that perception is tied to Trump's position in the polls, but it is clear that there's overlap between the groups most skeptical of Trump in regards to racial bias and those within his own party who are least supportive of his bid (which is to say: college-educated women). Shortly after Trump brought on new campaign manager Kellyanne Conway and Bannon as CEO, he started making direct overtures to black voters with the obvious aim of assuaging concerns about his perceived bias. His recent 180-degree flip on deporting immigrants who are here illegally is another example of his effort to change how people view him. (Conway, who has been a constant presence on cable news since her promotion, is clearly someone the campaign hopes will improve Trump's numbers with women.) There are 70-odd days until the election, and Trump is doing everything he can to give his base reasons to get on board with his campaign.

Clinton's team knows that. It knows what he's trying to do and it thinks it knows how to undercut it. Clinton's ad also isn't targeting nonwhite voters — she's hoping to remind wavering Republicans of one of the reasons they were wavering in the first place. Trump is hoping to drive past these concerns; Clinton is trying to toss an anchor around his trailer hitch.

This is Trump's main problem as the clock ticks down. Can he now, after a year-plus of making arguments that some racists did find appealing, redefine himself in the eyes of observers? We talked a lot about the media attention he attracted in the primary campaign and how that lifted him past his opponents. But everyone else was watching, too, and the perceptions they took away from it were clearly ones that are now unhelpful to his candidacy.

In 1964, MSNBC's Benjy Sarlin noted on Twitter, Lyndon Johnson made an ad in which a Klan leader was quoted as supporting Barry Goldwater. Johnson never used the spot, but Goldwater never shook the concerns voters had about his candidacy. Johnson won by 23 points.

Update: The Trump campaign released a response to the ad, signed by Pastor Mark Burns. It reads:

"Hillary Clinton and her campaign went to a disgusting new low today as they released a video tying the Trump Campaign with horrific racial images. This type of rhetoric and repulsive advertising is revolting and completely beyond the pale. I call on Hillary Clinton to disavow this video and her campaign for this sickening act that has no place in our world."