Donald Trump continued to fume over the Russia investigation on Sunday, more than a year after special counsel Robert Mueller filed his report without recommending charges against the president but only three days after the justice department said it would drop its case against Michael Flynn, Trump’s first national security adviser.

“The biggest political crime in American history, by far!” the president wrote in a tweet accompanying a conservative talk show host’s claim that Barack Obama “used his last weeks in office to target incoming officials and sabotage the new administration”.

The tweet echoed previous messages retweeted by Trump, which earned rebukes for relaying conspiracy theories. On Sunday afternoon the president continued to send out a stream of tweets of memes and rightwing talking heads claiming an anti-Trump conspiracy. One tweet by Trump simply read: “OBAMAGATE!”