But no one knows at this point the political leanings, if any, and motivations of the person who sent them. Teams of law enforcement officials will seek to answer those questions.
Trump and others in his Administration were quick to condemn the acts, calling them "despicable" and promising that the perpetrator, if found, would be prosecuted to the full extent of the law.
The speed with which Administration officials responded was important, as was the universal condemnation across the country. But even a moment when political leaders on both sides find common rhetorical ground cannot erase the reality of the times in which we now live.
This is a time of the politics of the apocalypse - an all-or-nothing view of the difference between winning and losing an election and of holding power or not holding it.
There is no middle ground on what winning or losing means.
This has been on the rise for a long time. But it has intensified of late. No one really knows how to roll it back. Politicians say that it is time for the country to come together. But on whose terms?
Political rhetoric has escalated dramatically, spurred by the ideological divisions and aided by social media.
This has created two Americas, and turned those in one America against those in the other.
Forces that not that long ago had been suppressed, though not eliminated, have been emboldened and unleashed. Racial antagonism, anti-Semitism and a more general fear of the opposition permeate at least a part of many political conversations.
Trump brands opponents as evil, a word from which many officials in his party recoil. But that characterisation finds support among many of his followers, who see a country under attack from what might be called otherness.
Democrats, offended and alarmed by so much of the Trump presidency, see the part of America that rallies around the President not just as people with different views but collectively as a threat to the very future of the country.
The threat of terrorism is real; it too is part of these times.
It has been that way, certainly since the attacks of September 11, 2001, and really before that.
With each such attack - Paris or San Bernardino, California, or on a baseball field in the Washington suburbs - the fear level rises.
Those reactions are real and are felt across the political spectrum. What politicians do with them is another matter.
Trump seizes on events and issues to stir images of a nation in danger of being overrun by terrorists, criminal immigrants, drug gangs or even left-wing activists.
He is a master of the art.
He praises a Montana politician who assaulted a reporter at a time when a contributing columnist to the Washington Post is killed, allegedly at the hands of a Saudi hit squad.
He brands at least some in the news media as enemies of the people.
He encourages those at his rallies to hector reporters in attendance.
He encouraged violence against protesters at some of his rallies in 2016.
He won the presidency by playing on cultural wedge issues as much as by focusing on economic worries.
This northern autumn, he seeks to prevent the loss of the Republicans' congressional majorities with rhetoric of the same kind.
The sizable caravan of Central Americans now in southern Mexico and heading north provides a timely foil, just as "bad people" from Mexico were his target the day he launched his campaign in 2015.
Democrats hate being called the party of open borders, but many of their leaders struggle to define a clear policy for those who come across the border without documentation.
Republicans took from their success in confirming Supreme Court Justice Brett Kavanaugh that branding Democrats as an angry mob could pay political dividends.
The jury is still out on that, but there is some evidence that the Trump base is more motivated than it was before Kavanaugh.
Trump offers no apologies for attacking Christine Blasey Ford, who accused Kavanaugh of a sexual assault when they were teenagers. "We won," the President says in explaining why anything goes. That's the measure of everything.
The President's opponents have sometimes succumbed to playing the game against him. Hillary Clinton declared that there can be no civility in politics as long as Republicans are in control. Former Attorney-General Eric Holder said that when Trump and Republicans go low, kick them. Defenders pass off these remarks as mere rhetoric and not to be taken literally. Trump's loyalists see it differently.
Some on the left have played into Trump's hands by hounding Republican officials - Senator Ted Cruz and his wife, and earlier, White House press secretary Sarah Sanders - in public places. Then, just days ago, the same thing happened to House Minority Leader Nancy Pelosi, D, who was chased into a building by angry protesters hurling insults and expletives.
In the two years since Trump was elected, little has changed in terms of the public divisions over his leadership.
He is as popular or unpopular as he was, give or take a few points in his approval ratings. The groups that liked or didn't like him have barely budged in their opinions.
Most presidents see their ratings ebb and flow, with good times and bad, with victories and setbacks, with good economies or bad.
Trump, with an economy running strong, has received little benefit. Things other than traditional fundamentals are dictating how people see the President and each other.
The shock of what was revealed today brought a moment of respite.
In remarks at the White House, Trump said: "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."
Earlier in the day, while campaigning for Democrats in Florida, Hillary Clinton issued a similar call, saying this is a time "to do everything we can to bring the country together".
This is what happens. Some events are too shocking for people to do anything other than condemn them.
But will any of that change anything about the final days of the Midterm elections, or the aftermath of those elections, or the next two years of the Trump presidency?
With so much at stake for those on both sides of the political divide, that question might be quaint or naive. Which is why the country is so much on edge.
