It can be one or both.
Examples:
I think Obama was popular because he's an intelligent, progressive and articulate person and followed on from a knuckle-dragger. The latter was also unpopular because of the Iraq war. (Tony Blair is regularly described by those on the left in the UK as being a war criminal).
Trump is viewed as a dangerous idiot, but you probably knew that.
No not at all responsible. The foreign interference in Brexit came from Russia (who obviously want the break up of the EU).
A lot of the UK trade is with Europe and our trade deals around the world are based on us being a part of the EU, a powerful trading bloc. So we got good deals and the EU upholds various standards (food, H&S...)
Out of the EU, as a single small island we will be desperate for deals and have no leverage or negotiating muscle (compared to being in the EU). So, going forwards, the government is looking for new trade deals. We've got one with Liechtenstein, next up, the US. The US are looking to move in on our public health service which will result in higher prices for the service (and hence the public) and it fits with the rightwing tory long-term agenda of privitisation (I'm going off on one here, aren't I). The other big worry for Brits is food standards. The example we all know about in the UK is chlorinated chicken. Not allowed within the EU but we'll be free (indeed forced) to accept such delights. And yes, trade deals can take years, although the lying brexiteers said (I kid you not) such things could be sorted out "in an afternoon over a cup of tea."
Right, that's done my blood pressure no good so I'll stop now and go out for a run....