One of the most famous and insightful lines Donald Trump offered on the campaign trail in 2016 came during a stop in Iowa, shortly before that state’s caucuses.

“I could stand in the middle of Fifth Avenue and shoot somebody and wouldn’t lose any voters, okay?” Trump said, mimicking firing a gun with his fingers. “It’s, like, incredible.”

It was a comment about the robustness of his base of support, and it repeatedly has been demonstrated to be true. But we’d like to now introduce a corollary that is also true: Trump could stand in the middle of Fifth Avenue and shoot somebody, and few of his voters would consider the ensuing murder trial legitimate.

Trump’s daughter-in-law Lara Trump appeared on Sean Hannity’s Fox News Channel talk show on Thursday, where she and the host discussed the newly robust House investigations of Trump’s campaign and businesses.

“I think that Democrats right now are showing how scared they are with the fact that [special counsel Robert S. Mueller III’s] report is probably going to be released soon, because they are frantic to find something else to throw at the president, to throw at anybody close to him,” she said. “That’s why he saw those 81 subpoenas last week. So ridiculous. And just — I mean — people should be shocked and appalled by this in our country. This is not how it’s supposed to work. Just because you’re still upset over an election that happened 2½ years ago, you should not be allowed to try and ruin people’s lives like this.”

She’s referring to 81 letters requesting more information that were sent to people and entities associated with the president in some way. (They were not subpoenas.) But notice how she contextualizes it: It’s a desperate move to whip up a fake controversy targeting her father-in-law. The Mueller inquiry is biased, the argument goes, and with its conclusion, more biased investigations are needed.

President Trump, of course, tweeted her comments.

Lara Trump is not an impartial observer here, both as a relative of Trump’s and as an adviser to Trump’s campaign. But it’s clear that her sentiment is shared. In December, Quinnipiac University found only 12 percent of Republicans thought the investigation of possible coordination between the Trump campaign and Russia was legitimate.

Trump has been deliberate from the outset of the Mueller investigation in trying to establish its illegitimacy and partisan bias. Polling from HuffPost and YouGov shows that, over the past year, views of Mueller’s efforts have remained static by party and by 2016 vote.

It’s an investigation that is most publicly associated with Mueller’s investigation — an inquiry that began in 2017 by then-Deputy Attorney General Rod J. Rosenstein, a Trump appointee.

This idea that investigations of Trump are illegitimate extends beyond those centered on the president. When the Manhattan district attorney announced 16 new indictments against former Trump campaign chairman Paul Manafort on Wednesday, a Republican consultant who spoke with the New York Times made clear how it would be framed.

“Any and every action even perceived to be a threat against him or his presidency will be framed as political retribution and an effort to undermine his 2016 victory,” he said — echoing Lara Trump’s later interview.

Trump has been pitching this product since his first month in office.

Manafort and Trump’s former personal lawyer Michael Cohen admitted to criminal acts, but Trump supporters either note those charges weren’t related to Trump or, in the case of the campaign-finance charges admitted to by Cohen, they weren’t actual crimes. Everything is trumped up and illegitimate until it isn’t, at which point it’s moved to an arm’s length.

One wonders what might break this spell. What might emerge from the House investigations that would be so damning as to give even Trump’s most fervent supporters pause? There may be nothing at all, of course, but this is a president who was sued for fraud in connection with his real estate “university” and whose machinations surrounding his nonprofit foundation were well known before the election. He was on tape bragging about groping women and then insisted that allegations he had groped specific women were all lies — and it doesn’t seem to have done much to dent his popularity in some quarters.

But what if it has shown that he committed insurance fraud, as Cohen intimated during congressional testimony? What if he actually did directly collude with an agent of Russia, the main qualifier identified by Trump fans as demonstrating collusion in an informal survey we conducted. Or something else? It would be an interesting political experiment if Trump were to shoot someone dead, how his base might respond to what happened next. We would nonetheless prefer he not undertake it.

What Trump was saying when he made that “Fifth Avenue” comment wasn’t just that his base was loyal. It was that he could hold their loyalty. It’s hard to believe that only 12 percent of Republicans would view the Russia investigation as illegitimate if Trump hadn’t been constantly harping on about its illegitimacy.