"Historical corruption (real or not) is irrelevant to any current corruption (real or not)."
Totally untrue. Past corruption is very likely to attempt to deny, avert and bury past acts of corruption when spotlighted.
"Trump was asking for a personal favor from Ukraine for his own benefit, it wasn't for US interests."
Repetition of this opinion doesn't make it any truer. Trump said "we" not "I", and the surrounding evidence in context also suggests that it is only meant as being on behalf of USA.
"if there is anything credible regarding the Biden's actions at the time, it should be reported to US authorities to assess and investigate if need be. "
Don't trouble yourself with this non-argument. The apparent discrepancies and issues are being handled, by accounts.
"How many instances in the history of the US can you name where a US President asked a foreign government to investigate a US citizen that was not under investigation by US authorities?"
The answer is expected to be at least one, even without Trump. You can wait and find out what I mean, if you don't already.
"Noting Trump didn't care if Biden was investigated or not, he was only concerned about it being announced for political reasons."
Once again, your opinion and interpretation of the narrative.
The game is up for the past corrupt players. Finito!
