IN A major speech Thursday, Hillary Clinton linked Donald Trump to bigoted elements on the fringe of American politics. But she got it wrong when she said, “Trump is reinforcing harmful stereotypes and offering a dog whistle to his most hateful supporters.”

It’s not a “dog whistle” if everyone can hear the bigotry.

Republicans supporting Mr. Trump, explicitly or tacitly, cannot reasonably claim that they do not know who he is and what he has been doing.

Before running for president, Mr. Trump was the king of the “birthers” who questioned President Obama’s place of birth. He started his campaign by calling Mexican migrants rapists, then spoke approvingly of the inhumane 1950s deportation program known as “Operation Wetback” and delivered a convention speech that described a country overrun by violent foreigners. As Ms. Clinton recounted, House Speaker Paul D. Ryan (R-Wis.) called Mr. Trump’s attack on a federal judge because of his Mexican heritage “the textbook definition of a racist comment.” Add in the Republican nominee’s proposed Muslim travel ban, his false aspersions on the U.S. Muslim community, his long history of belittling women, his dissemination of an anti-Semitic graphic, and a clear picture was visible long before Ms. Clinton approached the lectern.

In more recent days, Mr. Trump has attempted to salvage his image with appeals nominally aimed at African Americans. Instead, he only dug himself deeper, depicting African Americans as desperate people living in abject squalor with nothing to lose. He hired a new campaign chief executive, Stephen Bannon, a man who has called the Civil War the “war of Southern Independence” and who ran a website that warned the Obama administration is “importing more hating Muslims.”

Unsurprisingly, polling shows that a majority of Americans believe Mr. Trump is biased against women and minorities. Whether Mr. Trump is a genuine bigot or just cynically appealing to bigoted sentiment is not a question we can answer. Certainly not everyone who supports Mr. Trump is a bigot. But Mr. Trump has attracted the support of assorted American bigots, once thought ejected from mainstream U.S. politics. The candidate has courted this support with plainly visible winks and nods, retweeting their messages and hesitating to disavow them when asked. At any point — such as last August, when the New Yorker’s Evan Osnos pointed out that white nationalists were rallying to Mr. Trump’s cause — Mr. Trump could have offered the loud, full and unequivocal condemnation of the bigoted fringe that the situation required.

Ms. Clinton ended her Thursday speech by praising Bob Dole, George W. Bush and John McCain, all of whom, in critical moments, stood up to bigoted elements on the right. Unfortunately, Republican leaders are not showing as much mettle this year. Even two of the men Ms. Clinton praised, Mr. Dole and Mr. McCain, have endorsed Mr. Trump. They should reconsider the cost to their reputations and the nation’s well-being. Any rational accounting would show that it is far too high.