Shouldn't Biden and the Democrats reopen the investigation of Trump's ties to Russia during the 2016 election and thereafter . ?

Federal prosecutors in VA, DC and NYC are looking into it right now.

The Attorney General of the US could do just that.

If Biden did it, it would be seen as a political move, so Republicans would be up in arms. It has to be left to the attorney general.
When Obama was president the FBI warned of Russia meddling in the election to help Trump, but Obama stayed out of it, for the same reason.

Fugazy Theatre -    Have you ever read The Assessment Report?   It was put together by our US intelligence agencies.   HERE is the link:  
/tinyurl.com/hfpqasu  

So you disagreed with the mueller report? Sounds like you’re desperate 

I disagree with Barr's findings in the Mueller report . Rosenstein limited the investigation and prematurely ended it . There was no investigation of money laundering which is likely the main reason Trump showed favoratism toward Putin and Russia . After all , Trump is motivated by money and will go to no ends to enrich himself .