Well.... that is the absolute defining factor of Christianity.... is to admit your sins, repent, and turn away from them.
That is the whole Christian belief system at its very core. Repent, and have faith in Jesus.
If Donald Trump turned, and repented, and admitted faith in Jesus, that would be as much of a Christian as any human can achieve.
Have you met Trump. The guy doesn't admit a mistake, ever.
I'm not sure what your belief is about Christianity, but the Apostle Paul was a murderer. The reason G-d allowed him to write most of the new testament, and why we call him an Apostle of Jesus, is because he repented and turn his life to Jesus.
That's the entire thing dude. That's whole Bible in a nutshell. Repent and believe. If Trump did that, it would be more amazing than anything else he has ever done in his life.
Yeah, thing is, Christianity seems more about kissing God's ass than doing good works... kind of why I rejected it a long time ago.
As Mark Twain observed "If Jesus were here today, the one thing he wouldn't be is a Christian".