One of the most important questions in the Trump administration’s war on the FBI and the recent Nunes memo controversy is how Republican voters would respond to all of it. New data is shedding light on the answer to this question — and it’s not very promising.

According to a Reuters/IPSOS poll released on Monday evening, a huge majority of Republicans — 73 percent — believed that “members of the FBI and Department of Justice are working to delegitimize Trump through politically motivated investigations.”

There’s no evidence so far of such a massive, sweeping conspiracy theory — not in the Nunes memo, not in text messages between FBI employees released to the public, not anywhere. But it’s a theme that’s been repeated again and again by the president, conservatives, and Fox News — and apparently, most Republicans have gotten the memo.

The Reuters poll isn’t a one-off. A SurveyMonkey poll released over the weekend found that only 38 percent of Republicans have a “favorable” view of the FBI, while a plurality, 47 percent, have an unfavorable view.

This is a striking decline in GOP views of the bureau: In 2015, per Reuters, a huge majority of Republicans — 84 percent — reported favorable views of the FBI. A Huffington Post poll released last week also found a large decline in Republican views of the FBI from 2015 to today.

This is discouraging, because it indicates that many Republican voters are willing to believe whatever Trump and House Republicans are saying, regardless of its connection to actual facts. And that says something very troubling about the health of American democracy.

How partisanship threatens democracy

In their new book How Democracies Die, Harvard political scientists Steven Levitsky and Daniel Ziblatt analyze the strategies used by leaders who have taken over a democracy and turned it into an authoritarian state. They found three common tactics: seizing control of courts and security services, marginalizing prominent individuals in the opposition and civil society, and changing election rules to rig the game against their political opponents.

“Trump,” they write, “attempted all three of these strategies.”

Would-be authoritarian leaders often undermine democracy by mounting attacks on state institutions that are supposed to be neutral, like federal law enforcement and the courts. They attempt to turn them into a tool of the executive, rather than a check on their power.

No individual change like this, Ziblatt and Levitsky explain, destroys democracy. Instead, they quietly erode democratic norms until elections are no longer truly competitive — a process that’s often invisible to the public.

One of the best checks on this degradation, experts say, is public resistance. If there are large demonstrations or other forms of major public outcry when a leader takes undemocratic actions, then the would-be authoritarian can’t get away with their attempts to consolidate power.

We have indeed seen mass protest in the US. But the protesters are mostly Democrats — and the way the president and conservative media have twisted mainstream Republican opinion in the FBI saga is troubling. It shows that partisan identity in the United States can blind voters to creeping authoritarianism in their own party. It also shows that when confronted with a clear attempt to corral the FBI and undermine special counsel Robert Mueller’s investigation of the president, many Republicans will side with their president.

At a certain level, this isn’t surprising. Political scientists have found that partisanship plays a profound role in shaping the way that people understand facts about the world.

“Misinformation is much more likely to stick when it conforms with people’s preexisting beliefs, especially those connected to social groups that they’re a part of,” Temple University professor Kevin Arceneaux told me last year. “In politics, that plays out (usually) through partisanship: Republicans are much more likely to believe false information that confirms their worldview.”

This effect is especially troubling when dealing with a leader like Trump, who has authoritarian instincts. It makes his supporters blind to his excesses, to the threat he poses to basic American institutions, and likely to see moves that threaten the foundations of American democracy — like, say, firing FBI Director James Comey for pursuing the Russia investigation and being insufficiently “loyal” — as justified.

This is part of why Levitsky and Ziblatt ultimately conclude that partisanship and political polarization, and not Trump specifically, poses the greatest long-term threat to American democracy. Trump, so far, hasn’t succeeded in most of his attempts to undermine neutral institutions.

But strong partisan identities can blind people to the importance of political tolerance. They can make them inclined to see anything and anyone who poses a threat to their party — most notably the opposition — as an enemy that must be crushed. Today, it’s the FBI; tomorrow, it could be the Supreme Court, or the Democratic Party.

“When partisan rivals become enemies, political competition descends into warfare, and our institutions turn into weapons,” Levitsky and Ziblatt write. “The result is a system hovering constantly on the brink of crisis.”