Why dative plural in this sentence, and help with translation

Question

I'm having some trouble understanding some of the grammatical constructions found in the following sentence which was taken from an article entitled "горшки на коммунальной кухне". Here is the link: https://lenta.ru/articles/2016/12/30/usrfmilitary

Российским властям не впервой пользоваться методом «обнуления» накопленного в двусторонних отношениях негатива, когда, грубо говоря, все помои оптом сливаются за шиворот уходящей вашингтонской администрации, а отношения с новыми людьми начинаются с чистого листа.

First of all, why is Российским властям in the dative plural?

Secondly, I am not sure what role негатива plays in the first part of the sentence. Is it associated with накопленного? My attempt at translation is as follows: "the Russian government is not the first to use the method of equalization (not sure about translation of обнуления. I assume it to be something along the lines of maintaining nuclear parity from the context of the article) having been accumulated negatively in two-sided relations, when ,roughly speaking,....

Finally, I am not sure how to fit за шиворот into my translation of все помои оптом сливаются за шиворот уходящей вашингтонской администрации. My basic understanding is that all the "garbage" created by the Obama administration with Russia is "going out the door" once Trump comes into office. That is to say, there will be a clean slate once Trump and his people take over.

Answer 1

"This isn't the first time the Russian government has used the method of 'resetting' the negativity accumulated in mutual relations, when, to put it bluntly, all of the mud is poured wholesale [sic] behind the outgoing Washington administration's collar, while relations with the new people start with a clean slate."

Власти is often used as if it were pluralia tantum (cf. the authorities). It has a stronger implication of agency than власть, which usually refers to power/government/authority as an abstract concept, or else to a particular authority when it appears as a kind of presence, a thing to be dealt with; власти is a government as a doer of things or an active participant in something.

Не впервой is a way of saying someone (appearing in the dative form) has done the action referred to before, with the implication that they're either experienced at it or use it as a preferred m.o.

Негатив is an unpleasantly slangy-with-a-touch-of-vogue-word general term for, essentially, anything bad that's communicated.

когда, грубо говоря, все помои оптом сливаются за шиворот

That's some truly horrible style by someone who thinks they're being edgy when they're just being stylistically tone-deaf; I'm surprised someone actually wrote that, as opposed to said in a trascribed interview, where it would at least be excusable. Шиворот is a term for "collar" that mostly appears in the idiom за шиворот, which usually refers not to the metaphorical action here (tugging at someone's collar and dumping a lot of filthy liquid under their shirt) but to grabbing someone by the collar or scruff of the neck. Another idiom is шиворот-навыворот, a vernacular rough equivalent of "topsy-turvy" that's not seeing a lot of use these days.

Оптом is a particularly horrible word choice here — the deliberate kind of horrible, by someone who presumably congratulated themselves on what they thought was the energetic, p*ss-and-vinegar quality of their journalistic copy. Anyway, not to rant too much, the word is not used in this random kind of manner, even by people who don't care how they sound. It's just weird and clunky.

Обнуление is literally a reset to zero, semi-figuratively to a "clean-slate" state.

Answer 2

Is this translation more clear? I tried to use Dative in English too and translate as literally as I could.

Российским властям не впервой пользоваться методом «обнуления» накопленного в двусторонних отношениях негатива, когда, грубо говоря, все помои оптом сливаются за шиворот уходящей вашингтонской администрации, а отношения с новыми людьми начинаются с чистого листа.

To Russian authorities it is not new to use the method of "annulling" of the negative[things] collected in the bilateral relations, when, speaking rudely, all the garbage wholesale is thrown into the collar of the leaving Washington administration, and the relations with the new people are starting from a clean page.