@moonbus said
The justice dept. indicted Russian operatives on charges of manipulating the 2016 election, from Russia. Why shouldn’t they be able to investigate corruption charges against an American operating in Ukraine?
Announcing an investigation is pretty stupid, if you want to catch a thief. Announcing an investigation just gives the suspects chance to destroy evidence. That is exactly what debunks Trump’s claim that he was interested in combating corruption.
It depends on the rules. It's easier for me to state the rules for England and Wales and try to extrapolate to the US. This is what the Crown Prosecution says:
In cases involving England and Wales and other jurisdictions (including non-EU countries), the common law position is that an offence must have a "substantial connection with this jurisdiction" for courts in England and Wales to have jurisdiction. It follows that, where a substantial number of the activities constituting a crime takes place within England and Wales, the courts of England and Wales have jurisdiction unless it can be argued, on a reasonable view, that the conduct ought to be dealt with by the courts of another country (R v Smith (Wallace Duncan) (No.4) [2004] 3 WLR 229, per Lord Chief Justice Woolf).
https://www.cps.gov.uk/legal-guidance/jurisdiction
since this is under common law it is likely that the US would have similar rules and regard interference by Russian nationals as "a substantial connection" with their Jurisdiction.
British subjects may be tried for some offences wherever they are committed where a statute allows it [1]:
Sexual offences against children (s. 72 of the Sexual Offences Act 2003, amended by the Criminal Justice and Immigration Act 2008);
Offences listed in schedule 1 of the Suppression of Terrorism Act 1978, this includes murder, manslaughter, kidnapping, GBH, rape and some firearms offences;
Terrorism;
Fraud and dishonesty;
Bribery (The Bribery Act 2010)
According to the Wikipedia page the US has no such legislation [2]. This means that it is possible that the Department of Justice has no power to prosecute a US citizen for corruption in a foreign country, as it's not clear what the "substantial connection with this jurisdiction" is, other than Biden's nationality. Ukraine, on the other hand, can investigate, and it would be a lot easier for them to do it.
It's easy for me to be wrong about this as I may have misunderstood UK law and I'm on dicey grounds trying to extrapolate to the US, but I knew where to look for the UK rules.
[1] https://www.cps.gov.uk/legal-guidance/jurisdiction
[2] https://en.wikipedia.org/wiki/Universal_jurisdiction#United_States