Trump seeks DOJ investigations into Obama Admn

US President Donald Trump today sought an investigation into his predecessor Barack Obama's Administration for not doing something to stop the alleged Russian interference into the 2016 elections.
Last week Special Counsel Robert Mueller charged 13 Russians individuals and three companies with meddling in the 2016 presidential elections.
Democrats say that this benefited Trump, a claim refuted by the president.
Trump has consistently argued that such an alleged interference happened during the term of a Democratic president and thus this needs to be investigated.
As such he posed a question in this regard on twitter.
"Question: If all of the Russian meddling took place during the Obama Administration, right up to January 20th, why arent they the subject of the investigation? Why didnt Obama do something about the meddling? Why arent Dem crimes under investigation? Ask Jeff Sessions! Trump tweeted.

Sessions is his Attorney General and heads the Department of Justice which is responsible for all such investigations.
Mueller has so far interviewed several of the Trumps former and present campaign officials.