There are two things to point out here:
1) With Joe Biden running for president in 2020, President Donald Trump should not have directly involved himself in any investigation of Biden, because Trump had too much to gain professionally from the outcome of such an investigation. Such involvement by the president (who would have a personal stake in the outcome) would not accord Biden equal justice under the law. Sen. Lamar Alexander explained this very well in his statement on impeachment.
2) President Donald Trump also should not have withheld military aid to the Ukraine, previously authorized by Congress, in order to encourage such an investigation. President Trump simply should not have involved the messiness of American politics in the serious business of foreign affairs - but he did. Once again, Sen. Lamar Alexander covered this in his statement.
There is nothing wrong with investigating Joe Biden and/or his son, Hunter. However, President Trump should not have directly involved himself in any such investigation. If the conduct of Joe Biden and/or his son warranted an investigation, it should have been left up to the Attorney General, William Barr and the Director of the FBI, Christopher Wray to investigate. President Trump should have stayed out of it... but it is clear in the transcript of the July 25th phone call with President Zelensky of the Ukraine, that he didn't.
I disagree; it is illogical to say the person delegated constitutionally to see law faithfully executed, is the only guy in the country who can't blow a whistle because the other guy may or may not be his opponent in the general election. The Bidens are *only* being scrutinized NOW because ONLY Trump brought attention to it. Well, actually Democrats brought the attention to it by manufacturing a Ukraine-based impeachment.
This is yet another instance, the firing of Comey being another, that the president exercising his plenary powers is grounds for criminal indictment or impeachment by radical factions, if he's a Republican. If a couple of psychologically damaged women notified the WH that Biden got real rapey with them in college, should Trump notify someone of that, or not because Biden is a candidate? Of course he should.
Then neither can Obama/Biden withhold or threaten to withhold aid that congress has approved, right? No, they're Democrats.
We agree Biden can be investigated and now he is because Dems wanted to fabricate an impeachable offense.