Participants gather during a special Memorial Day observance at the National World War II Memorial on Monday in Washington. (Toya Sarno Jordan/Reuters)

Visiting the National World War II Memorial on Memorial Day made me reflect on the colossal sacrifice of the Greatest Generation. Four hundred thousand of them died in less than four years — too many to list individually, as the Vietnam Veterans Memorial does. They are symbolized by a wall of stars, each star representing 100 lives snuffed out far too young. But I was struck, too, by the unshakable national unity despite, or perhaps because of, such terrible suffering. And that unity did not end when the war ended in 1945.

Sure, there were bitter partisan divisions after World War II, with McCarthyists accusing Democrats of disloyalty. But the veterans who returned to Washington — including Dwight Eisenhower, Richard Nixon, John F. Kennedy and Lyndon Johnson — also had a sense of shared purpose that allowed them to do really big, really important things for our country. All of the major bills in the next 20 years — aid to Greece and Turkey in 1947; the Marshall Plan in 1948; the North Atlantic Treaty in 1949; the 1956 Federal-Aid Highway Act; the 1964 Civil Rights Act; the 1965 Voting Rights Act; the 1965 Immigration and Nationality Act; and the 1965 Social Security Amendments creating Medicare and Medicaid — were passed by enormous bipartisan majorities.

It’s hard to imagine that such unity was ever possible given that today major legislation, such as President Barack Obama’s Affordable Care Act and President Trump’s tax bill, routinely passes without a single vote from the opposition party. Both parties have become more ideological, with Democrats having lost the support of conservative Southerners — and Republicans having lost the support of liberal Northeasterners. The rise of social media and competing television channels (Fox for conservatives, MSNBC for liberals) encourage the demonization of the opposition party.

From the liberal side, you have a California college professor, Randa Jarrar, exulting in the death of first lady Barbara Bush, writing that she was “happy the witch is dead” because she “raised a war criminal.” From the conservative side, you have radio talk-show host Bill Mitchell tweeting: “The modern #DemocratParty is no less an enemy of America than #NaziGermany or #CommunistRussia was. They seek our complete and utter destruction as the greatest nation on earth.” This is the kind of irrational hatred that rips a democracy apart and makes self-government impossible.

But while there is certainly fault on both sides, I don’t want to engage in false equivalence by suggesting Republicans and Democrats are equally to blame. Republicans are far worse. They are led by a president who engages in the kind of toxic partisanship we have seldom, if ever, seen from the Oval Office.

Consider the tweet that Trump posted on Friday: “Democrats are so obviously rooting against us in our negotiations with North Korea. Just like they are coming to the defense of MS 13 thugs, saying that they are individuals & must be nurtured, or asking to end your big Tax Cuts & raise your taxes instead.” He is not just disagreeing with Democrats; he is impugning their motives. This follows his accusation that Democrats are guilty of “treason” and that “they certainly don’t seem to love our country very much.”

Not even Memorial Day — a time when the whole country should come together — could make Trump stop spreading his partisan poison. He posted three tweets that day repeating his bogus accusations that the FBI implanted a spy in his campaign for political reasons. This is widely and rightly seen as a cynical attempt to discredit the investigators who are probing Trump’s campaign. But like Trump’s previous accusations that he was wiretapped by Obama and that Obama’s aides unmasked the names of Trump aides in surveillance transcripts, this is also an accusation of criminality against his Democratic predecessor. With no factual support, the president claims that the “Obama Spying Scandal” could be “one of the biggest scandals in history!” This is deranged — and dangerous for a democracy where ultimately Democrats and Republicans must come together to solve our problems.

The irony is that Trump is not a loyal Republican. He has belonged to both of the main parties as well as to the Independence Party. When he was elected, many conservatives feared (and liberals hoped) that he would transcend the partisan divide. Instead he has reinforced it. He isn’t doing so for the sake of ideology; he has no coherent ideology. He does everything for personal advantage. He views all criticism as disloyalty that must be punished, and he calculates that his political survival depends on mobilizing the GOP base.

My fear is that Trump’s toxic partisanship will lead Democrats to retaliate in kind, polarizing the country even further. We are locked in a cycle of mutual-assured destruction. Like the Hatfields and McCoys, each side nurtures its hatred long after the original causes are all but forgotten. Republicans are still smarting over the nomination hearings of Robert Bork in 1987, Democrats over the impeachment of Bill Clinton in 1998. We need to summon the spirit of the Greatest Generation and overcome our partisan enmity. Otherwise we will fall to the most insidious enemy we have ever faced: domestic division.