“The damage being done is twofold,” Dolan wrote by email:

The president’s strategy is doing permanent damage to the view of law enforcement agencies, at least among the segment of the population that takes what he says as truth.

This is only part of “the more general problem we are having today with the success Trump and others have had in creating the view that there is no objective truth,” Dolan argued:

The manipulation of the truth by the president and other Republicans continues to degrade public discussion of issues.

While polarization has created a political universe composed of two truths, one Democratic, the other Republican, Trump has driven, and profited from, this duality.

“Am I concerned that Trump’s attacks on the Department of Justice, the F.B.I. and the ongoing investigations into collusion may undermine fundamental institutions and norms including the rule of law?” Shanto Iyengar, a political scientist at Stanford, wrote me by email. “For sure.”

Iyengar posed the following hypothetical:

Let’s assume that Mueller uncovers evidence of collusion and close associates of the Prez are implicated. Republicans are likely to deny the validity of the charges on the grounds that the investigators are biased and Republicans in Congress, as they’ve repeatedly demonstrated, will stick by Trump since the base is with him. Trump, of course, will continue with the ‘hoax’ narrative, and his surrogates in the media will be only too happy to back him up. At that point, we will have a very real threat to the rule of law.

Trump’s attacks on the F.B.I. are a case study in his polarization strategy. Since its founding in 1908, the F.B.I. has had substantial popular support, especially among Republicans. Historic poll data is revealing. A 1949 Gallup poll asked “What is your opinion of the F.B.I.?” 41 percent said “very high, excellent, it does wonderful job,” and 53 percent said “good, approve of it,” for a total of 94 percent. Three percent voiced “mild disapproval,” and the responses of 1 percent were “derogatory.”

More recently, the NBC News/Wall Street Journal poll tracked partisan views of the F.B.I. from December 2014 to January 2018. Over that three-year period, the percentage of Democrats voicing “a great deal or quite a bit of confidence” in the agency rose from 34 to 53 percent.

Republican confidence moved in the opposite direction, from 46 to 31 percent.

Just this month, a February 1-2 Survey Monkey poll sponsored by Axios found that favorable views of the F.B.I. among Republicans — putatively members of the law-and-order party — had fallen to 38 percent, while a plurality, 47 percent, disapproved. Among all voters, 49 percent approved of the F.B.I. and 28 percent disapproved; Democrats were favorable by 64-14.

Alex Theodoridis, a political scientist at the University of California-Merced, wrote me:

Polarization by party identity is so powerful at the moment that most voters see the world through thick red and blue lenses. Almost everything is politicized. And, in almost every study I have run, I find that Republicans are more intense partisans than Democrats on average. We’ve seen partisanship color Republican evaluations of the FBI (negatively) and Russia and Putin (positively).

Theodoridis argued that the damage to “any given institution is not likely to last beyond its usefulness in a specific political context.” But, he warned,

the more pernicious problem is the very phenomenon of universal politicization. If everything, even the most esteemed institutions and norms, is subjected to the power of partisan motivated reasoning, then there really cease to be esteemed institutions and norms.

Moving from politicization to politics, how likely are these trends to play out in the midterm elections?