Soliciting foreign influence into elections is illegal under the American Constitution. Whether its for this election or a previous one doesn't make it any less illegal. That Biden is also a current political foe meant that Trump should've been extra careful, besides, if he wanted Biden investigated, he has his Attorney General (who is just as much a Trump sycophant) to hold the investigation, He didn't need and should not have asked Ukraine to do this.
So unfortunately, whilst you may feel this or that about it, the letter of law is clear, and Trump violated it, and his supporters have basically moved from a position of "he didn't" to" so what?"