I will answer these together because you are conflating two separate matters.
Obama, through Biden, who was a legitimate emissary of the United States, to work with other allies to force the corrupt prosecutor in the Ukraine out of office. This was hailed as an achievement by everyone concerned. The purpose was to combat corruption, which is America's national interest.
You falsely equate that to Trump, sending his personal lawyer, who has no legal standing to speak for the United States, to pressure the Ukraine to aid and assist in Trumping up charges against Biden, for the purpose of helping Trump's re-election.
Those are not the same thing and that should be obvious. But if you can't get it, I spell it out.
Trump, through Giuliani, is soliciting a foreign leader to assist him in his re-election. If this sounds familiar, it is.
Giuliani is not a legitimate emissary of the United States and can't bind the U.S. Anything he spoke about was in the shadows, the way the mob works. 'It sure would be a shame if the U.S. held up your military aide because your country. Maybe you should investigate Mr. Biden?'
There is no hint, except from right-wing conspiracy sites, that Joe Biden did anything unethical. He was acting on the interests of the United States in the open, not in the shadows.