If I were to choose the best single word, a "post-truth" [communications] strategy is probably it, although what is new about it are apparently not its elements, but its intensity.
Probably not entirely analogous but a similar PR strategy is
Fear, uncertainty, and doubt (FUD)
is a disinformation strategy used in sales, marketing, public relations, politics, cults, and propaganda. FUD is generally a strategy to influence perception by disseminating negative and dubious or false information and a manifestation of the appeal to fear.
FUD doesn't quite seem to have an explicit "admit but deny significance" phase though, at least as usually conceptualized. On the other hand, that part is more formally called minimization
Minimisation is a type of deception involving denial coupled with rationalisation in situations where complete denial is implausible. It is the opposite of exaggeration. Minimisation—downplaying the significance of an event or emotion—is a common strategy in dealing with feelings of guilt.
Minimization, denial, and blaming [the victim or circumstances] are also clearly recognized in research and practice with sexual offenders. [...]
The simplicity of the phrase denial, minimization, and blaming belies considerable complexity in definition. Although a single underlying construct
may link these terms conceptually, the terms denial, minimization, and blaming represent at least two dimensions. The first is a continuum ranging from
outright denial of engaging in actions that are abusive to an intimate partner
to clear and complete admission of abusive actions and their consequences.
Denial and minimization fall along this continuum. Examples include outright denial of abuse, minimization of specific abusive actions (e.g., a light
push is reported rather than an injury-causing shove), and admission of acts
with denial of impact (e.g., acknowledgment of a slap with assertion that the
victim had no reason to fear or to be upset in response). Blaming, by contrast,
refers to the attribution of causality to factors outside the self. For example,
an individual who acts in an abusive manner may “blame” his or her actions
on the behavior of the partner (e.g., “If you hadn’t . . . then this wouldn’t have
happened”) or on the circumstances (e.g., “This would never have happened
if your friends didn’t interfere”).
So this is hardly a communication/psychological strategy unique to politics. It probably can be used anytime someone is accused of something.
And while this is not a strategy per se but an umbrella term, post-truth politics covers it in the political realm:
Post-truth politics (also called post-factual politics and post-reality politics) is a political culture in which debate is framed largely by appeals to emotion disconnected from the details of policy, and by the repeated assertion of talking points to which factual rebuttals are ignored. Post-truth differs from traditional contesting and falsifying of facts by relegating facts and expert opinions to be of secondary importance relative to appeal to emotion. While this has been described as a contemporary problem, some observers have described it as a long-standing part of political life that was less notable before the advent of the Internet and related social changes.
[...] In 2016, post-truth was chosen as the Oxford Dictionaries' Word of the Year due to its prevalence in the context of that year's Brexit referendum and media coverage of the US presidential election. [Also] In December 2016 "postfaktisch" (post-factual) was named word of the year by the Gesellschaft für deutsche Sprache (German language society), also in connection with a rise of right-wing populism.
Some authors do point out that it's not actually that new in politics:
However, the phenomenon of political actors spreading false information – as a strategy in the pursuit of support or as a smokescreen to divert attention away from unwanted information or unpopular policy actions (Alterman, 2004, Lewandowsky et al., 2017) – is not new. Schudson (2009) discusses the term truthiness which was introduced in a Comedy Central satirical tv-show and which at first referred to the way the Bush administration justified the invasion in Iraq. He points out that the concept of truthiness was not new either, and refers to Hannah Arendt’s essay Lying in Politics (1971) in which she accused the administrations of the presidents Johnson and Nixon of defactualization. Similarly, Allcott and Gentzkow (2017) discuss a number of historical examples of partisan conspiracy theories, like those concerning the assassination of Martin Luther King (1975) or the denial of Nazi extermination of millions of Jews (1994).
On the other hand, what seems new is the scale at which they were employed in recent years:
While terms like defactualization and truthiness have become common in the study of political communication, the new terms post-truth and alternative facts seem to indicate that new lines are being crossed and that politicians do not even pretend to communicate truthfully anymore. The 2016 U.S. presidential campaign is no doubt one of the best known illustrations of post-truth politics. According to the independent fact checking website PolitiFact, 70% of the statements by Donald Trump were (mostly) false. His opponent, Hillary Clinton, was found to deviate from the ‘truth’ in 26% of all cases (Politifact n.d.). Gibson (2018) argues accordingly:
[T]he path to a Trump presidency was forged out of a series of racist slanders, demonstrably false statements, and unproven conspiracy theories: Barack Obama was born in Kenya. Immigrants are criminals and rapists. Climate change is a hoax. Mexico will pay for the wall. The falsehoods, exaggerations, and demagoguery flow like water from a firehose. They stun and bewilder. Worse, they distract and immobilize—which, of course, is precisely the point.
[...] Following Dean, 2010, Andrejevic, 2013, Gibson, 2018 summarizes three rhetorical strategies which emerge from, and take advantage of, the ‘post-truth double helix’: (1) ‘the proliferation of narratives’, which may produce confusion, uncertainty and, ultimately, democratic fatigue and immobility, (2), ‘the politicization of expertise’, rendering all forms of knowledge (including science) subject of endless debate and (3) ‘the cultivation of conspiracy’, as an attempt to reconstruct order in the chaotic context of claims and counter-claims. In short, a context that renders it increasingly difficult for the audience to distinguish between facts and disinformation and trustworthy and unreliable voices, allows for the most deceptive forms of political persuasion.
And Wikipedia mentions (citing Politifact and the Washington Post) that
[Trump] has a pattern of making controversial statements and subsequently denying having done so. By June 2019 many news organizations had started describing some of Trump's falsehoods as lies, and that he has repeated some falsehoods so many times that he has effectively engaged in disinformation.
For the last point, the citation is WaPo's introduction of the "bottomless pinocchio" rating in Dec 2018.
Trump’s willingness to constantly repeat false claims has posed a unique challenge to fact-checkers. Most politicians quickly drop a Four-Pinocchio claim, either out of a duty to be accurate or concern that spreading false information could be politically damaging.
Not Trump. The president keeps going long after the facts are clear, in what appears to be a deliberate effort to replace the truth with his own, far more favorable, version of it. He is not merely making gaffes or misstating things, he is purposely injecting false information into the national conversation.
To accurately reflect this phenomenon, The Washington Post Fact Checker is introducing a new category — the Bottomless Pinocchio. That dubious distinction will be awarded to politicians who repeat a false claim so many times that they are, in effect, engaging in campaigns of disinformation.
The bar for the Bottomless Pinocchio is high: The claims must have received three or four Pinocchios from The Fact Checker, and they must have been repeated at least 20 times. [...]
The Fact Checker has not identified statements from any other current elected official who meets the standard other than Trump. In fact, 14 statements made by the president immediately qualify for the list.
As for Trump denying have said some things, Wikipedia points to a (2016) Politifact article that gives some (17) examples. There were more examples after that, e.g. in January 2019:
In 2016, Trump even said specifically that Mexico would be compelled to give the U.S. a “one-time payment” of $5 to 10 billion for the wall, both in a memo sent to reporters and in his campaign platform.
But as he prepared to fly to the southern border on Thursday, Trump changed his tune, claiming, falsely, that he never said that Mexico would pay for the border wall and that he never meant that the country would literally hand the U.S. money for the wall.
“When during the campaign, I would say ‘Mexico is going to pay for it,’ obviously, I never said this, and I never meant they’re gonna write out a check, I said they’re going to pay for it. They are,” Trump said.
Trump's numerous claims about Mexico paying for the wall (86 according to WaPo's count in Dec 2018) were one of the main reasons they introduced the "bottomless pinocchio" rating. So this is basically what others, more academically, call "post-truth".