Many details have yet to emerge about the pipe bombs that targeted Barack Obama, Hillary Clinton, Eric Holder, John Brennan, Debbie Wasserman Schultz, and George Soros. Mercifully, the Secret Service intercepted two of the packages, and none of the others exploded. So far, nobody has come forward claiming to have been the sender. Until that happens, or the F.B.I. nabs the perpetrator, caution should be exercised in attributing responsibility. But a few things are already clear.

One is that all of the targets were people whom Donald Trump has lambasted in his campaign rallies and outpourings on Twitter. They are also people who have been subjected to hateful abuse online by Trump supporters and alt-right groups. (In the case of Soros, as my colleague Eric Lach pointed out earlier, the attacks aren’t limited to the United States, and they go back years.)

We also know that the package to Brennan was sent to CNN, which Trump has repeatedly demonized, calling it “fake news” and “the enemy of the American people.” He has used the same inflammatory language about other news organizations, and, on occasion, he has appeared to encourage his supporters to take matters into their own hands. Last week, at a rally in Montana, he showered praise on a Republican congressman, Greg Gianforte, who, last year, assaulted a reporter for the Guardian. “Any guy that can do a body slam, he’s my kind of—he’s my guy,” Trump said, to loud cheers.

In reacting to the news about the pipe bombs, the White House didn’t mention any of this, of course. “These terrorizing acts are despicable, and anyone responsible will be held accountable to the fullest extent of the law,” Sarah Huckabee Sanders, the White House press secretary, said in a statement. Trump initially stayed away from the cameras. Then, on Wednesday afternoon, speaking at a White House meeting on the opioid crisis, he said, “The full weight of our government is being deployed to conduct this investigation and bring those responsible for these despicable acts to justice.” He added, “I just want to tell you that in these times we have to unify. We have to come together and send one very clear, strong, unmistakable message that acts or threats of political violence of any kind have no place in the United States of America.”

This statement of principle was welcome, if long overdue. But, unless Trump follows up by changing his behavior and his rhetoric in a fundamental way, his words will prove to have been empty. Will he now cease his attacks on the media? “The President, and especially the White House press secretary, should understand their words matter,” Jeff Zucker, the president of CNN, noted in a statement. “Thus far, they have shown no comprehension of that.” Actually, Zucker’s reading was a generous one. In targeting journalists and news organizations, Trump may well understand exactly what he is doing, and the dangers it entails. Nothing in his prior record suggests that he will alter course. Will he tone down his rhetoric in other ways? Will his supporters refrain from spreading baseless claims about Soros, the latest of which was that he had helped organize the caravan of refugees from Honduras?”

There are plenty of grounds for skepticism. Even before Trump spoke, some right-wing pundits and provocateurs were busy spreading another outrageous conspiracy theory. “These ‘Suspicious Package’ stories are false flags, carefully planned for the midterms,” Jacob Wohl, a Trump supporter and a writer at the Web site The Gateway Pundit, wrote on Twitter. The Daily Beast reported that Frank Gaffney, a former Reagan Administration official, and Michael Flynn, Jr., the son of Trump’s former national-security adviser, had voiced similar opinions. On his daily radio show, Rush Limbaugh muttered, “It’s happening in October. There’s a reason for this.”

We shall see what the investigation turns up. But we don’t need the F.B.I. or the Secret Service to inform us that, for years now, Limbaugh and his fellow Trump followers have been busy creating a feverish political environment in which outlandish and defamatory conspiracy theories routinely get propagated and believed—from “Pizzagate” to the latest Soros slur. We should also be well aware, by now, that in a country as divided and media-saturated as the United States the dividing line between political incitement and deadly violence is dangerously thin.

On December 4, 2016, Edgar Maddison Welch, a twenty-eight-year-old from North Carolina, turned up at the Comet Ping Pong pizza restaurant, in Washington, D.C., and fired a shot from a semi-automatic rifle, terrifying the staff and patrons. He later said he was convinced that the restaurant was involved in a child-sex ring tied to Hillary Clinton, a baseless theory he had picked up online.

On August 12, 2017, in Charlottesville, Virginia, James Alex Fields, Jr., a twenty-year-old from Ohio who had espoused white-supremacist beliefs, drove his Dodge Challenger into a crowd protesting against a Unite the Right rally, killing Heather Heyer, a thirty-two-year-old paralegal who was part of a counter-protest. Fields has been charged with second-degree murder and hate crimes.

Two months earlier, James Hodgkinson, a sixty-six-year-old resident of Belleville, Illinois, who supported Bernie Sanders and had called Donald Trump a “traitor” online, walked onto a ball field outside the Y.M.C.A. in Alexandria, Virginia, and opened fire at members of a Republican congressional baseball team. Steve Scalise, the third-ranking member of the House Republican caucus, was critically wounded, and two members of the Capitol Police, among others, suffered lesser wounds.

To many people who knew them, Welch, who is serving a four-year prison term; Field, who is awaiting trial; and Hodgkinson, who was shot dead by the police during his attack, seemed like unremarkable people. In a heavily armed nation of three hundred and twenty-five million people, it is frightening to think about how many other folks could follow a similar path to violence if the United States continues on its current trajectory under its current leader. (The fact that Hodgkinson espoused liberal beliefs was a reminder that, in a febrile environment of hatred and animosity, it isn’t only right-wingers who can become unhinged.)

A few days after the clashes in Charlottesville, my colleague Robin Wright interviewed Keith Mines, a former member of the U.S. Special Forces who has extensive experience in countries wracked by violent internal conflicts, including El Salvador, Iraq, and Afghanistan. Identifying some of the precursors to such conflicts, Mines pointed to entrenched polarization, weakened political institutions, irresponsible political leadership, and the legitimization of violence. “We keep saying, ‘It can’t happen here,’ ” Mines said, “but then, holy smokes, it can.” On a day like this, we barely need reminding.

An earlier version of this post misstated the location of the congressional baseball game.