New Jersey Rep. Jeff Van Drew didn’t win any valentines from Democrats when he left the party last month. One candidate for Van Drew’s congressional seat, Brigid Harrison, called him a “traitor” for pledging fealty to the GOP and Donald Trump on the eve of the president’s impeachment. Other Democrats denounced Van Drew as a turncoat and a coward, vowing to turn him out of office in the next election.

But nobody pledged to kill him, fortunately, which marks an important difference between our political parties. If Van Drew had been a Republican who defected to the Democrats, he would face threats to his life, not just to his job. And that’s a threat to democracy itself, which simply cannot function under conditions of fear and intimidation.

Consider the fate of Susan Collins (R., Maine), one of the Senate’s most moderate Republicans. During the 2018 confirmation hearings for Supreme Court nominee Brett Kavanaugh, Collins received a fax from someone promising to slit her throat if she voted for Kavanaugh.* Such a threat shows that unacceptable hatred and violence can come from both ideological sides.

But only one party — the GOP — has a leader who openly encourages such behavior: President Trump. And even among the dozens of Republicans who have left office since Trump was elected, just a handful of them, including Jeff Flake and Bob Corker, openly condemned the president on the way out. But most departing GOP politicians have kept quiet about Trump in their retirements, holding their tongues and their noses at the same time.

Maybe that’s the safest thing to do. During the Kavanaugh hearings, an anonymous caller threatened to kill Flake and his family for “interfering” with Trump. “I mention this with reluctance, but only to say we have lit a match,” Flake told the hearing. “The question is, do we appreciate how close the powder keg is?”

And it isn’t just public officials who are in danger; so are journalists. As depicted in the recent movie Bombshell, Fox News host Megyn Kelly got death threats after questioning Trump at a GOP presidential debate about his views of women.

“When Donald Trump comes after you, it isn’t just a tweet,” Kelly told an interviewer after the death threats, which led Fox to provide her with an armed security guard. “He has such power that a single tweet can unleash hell in somebody’s life.”

And that’s the key engine of violence in American political life right now: Donald Trump himself. He has encouraged people at his political rallies to assault protesters, promising to pay the resulting legal bills. And he hinted at the assassination of his 2016 rival, Hillary Clinton, warning that “Second Amendment people” might gun her down to prevent her from appointing liberal judges.

No wonder that three-quarters of people charged for making threats against American politicians come from the right, according to a 2018 analysis by the Prosecution Project. Yes, a Bernie Sanders supporter opened fire at a 2017 GOP congressional baseball practice, injuring Rep. Steve Scalise (R., La.) and three others. But no Democratic leader has openly encouraged attacks on opponents, as President Trump has done.

Most of all, no leading Republican politician has forcefully and consistently denounced Trump. We’re talking about a guy who has condemned his GOP critics as “human scum,” which must be catnip to his violent followers. Would you break with him, if you knew it might put your life in peril?

Van Drew doesn’t have to worry about that because he defected from the Democrats. But any Republican officials who are brave enough to leave the GOP will have to look over their shoulders, wondering who might want to take them out. If you think we can have a real democracy on those terms, think again. The real question is what we will do to save it.

Jonathan Zimmerman teaches education and history at the University of Pennsylvania. He is the author of “The Amateur Hour: A History of College Teaching in America,” which will be published in 2020 by Johns Hopkins University Press.

*A previous version of this piece incorrectly stated that Susan Collins received a fax from someone promising to slit her throat if she voted against Brett Kavanaugh’s nomination.