US President Donald Trump has challenged Attorney General Jeff Sessions to launch a probe into his predecessor Barack Obama's administration for failing to do enough to stop the 2016 election foreign interference, the media reported.Trump's Wednesday remark was the latest in a series where the President has faulted Obama for not doing enough to stop Russian meddling. But it was the first time Trump suggested that Sessions was not doing enough, reports CNN."Question: If all of the Russian meddling took place during the Obama Administration, right up to January 20, why aren't they the subject of the investigation?" Trump tweeted. "Why didn't Obama do something about the meddling? Why aren't Dem (Democratic) crimes under investigation? Ask Jeff Sessions!"Trump and Sessions were in the Oval Office together on Tuesday during an event honouring law enforcement officials.The two, according to a source, did not interact much while taking photos, reports CNN.Trump has nursed a grudge against Sessions ever since the former Alabama senator decided to recuse himself from all Justice Department investigations into the 2016 campaign, including the ongoing Russia probe.