CHARLESTON, S.C. — Democratic presidential candidates lashed President Trump on Wednesday with their sternest denunciations yet of his exploitation of racism for political purposes and his resistance to gun control, in a day of biting criticism that also highlighted differences between Democrats over how best to understand the recent rise of hate crimes in America.

More than ever, it was clear that last weekend’s massacres in El Paso and Dayton, Ohio, had put Trump on the defensive and added fierce new urgency to Democratic efforts to engineer his ouster. Trump has not accounted for the echoes of his own rhetoric about immigrants and minorities in the manifesto composed by the anti-immigrant gunman in Texas, and on Wednesday morning he appeared far more focused on feuding with his critics in the Democratic Party and the media than on striking a tone of healing.

Former vice president Joe Biden, in one of the most fiery speeches of his campaign so far, argued that Trump had “fanned the flames of white supremacy in this nation’’ with both explicit and implicit language as president.

“Trump readily, eagerly attacks Islamic terrorism but can barely bring himself to use the words ‘white supremacy,’ ’’ Biden said Wednesday afternoon in Burlington, Iowa. “And even when he says it, he doesn’t appear to believe it. He seems more concerned about losing their votes than beating back this hateful ideology.’’

Speaking in Charleston, S.C., at Emanuel African Methodist Episcopal Church, where a white supremacist gunman killed nine black worshipers in 2015, Senator Cory Booker of New Jersey also blamed Trump for encouraging hatred. The weekend’s violence, he said, was “sowed by those who spoke the same words the El Paso murderer did, warning of an ‘invasion,’ ’’ a word Trump has used to describe migrants approaching the Southern border.

Trump has emphatically denied that he is racist, and on Wednesday, he dismissed reporters’ questions about the role of his rhetoric in dividing the country, saying his language “brings people together.’’

For both Trump and his Democratic challengers, the extraordinary focus this week on white nationalism, gun violence, and domestic terror appeared to reframe a chaotic presidential campaign — at least temporarily — as a searing moral debate about the racial history and cultural destiny of the United States.

Trump, who rose to power railing against the country’s changing ethnic and cultural texture, contends that Democrats should be punished for opposing his immigration policies and rejecting the values of the rural white people who make up his political base. Democrats, meanwhile, are now arguing in the most explicit terms yet that white supremacists are receiving aid and comfort from the president of the United States.

“His low-energy, vacant-eyed mouthing of the words written for him condemning white supremacists this week I don’t believe fooled anyone, at home or abroad,’’ Biden said, referring to Trump’s remarks Monday about the El Paso shooting.

Insistently branding Trump as a figure who offends the nation’s political values, Biden contrasted the president’s ambivalent response to racism and tragedy with the conduct of his predecessors — Bill Clinton’s soothing response to the 1995 bombing at a federal building in Oklahoma City, for instance, and George W. Bush’s visit to a mosque after the terror attacks of Sept. 11, 2001.

In a biting one-liner that has become a regular jab on the campaign trail, Biden said to applause that Trump had “more in common with George Wallace than he does with George Washington.’’

Booker eschewed that kind of nostalgia for the Founding Fathers in his own speech against violent racism.

He said instead that white supremacy had been “ingrained in our politics since our founding,’’ within the text of the Declaration of Independence and the Constitution.