Donald Trump. Pic/AFP

Senior Democrats have warned President Donald Trump not to use a controversial memo as a "pretext" to fire the special counsel probing alleged Russian involvement in the 2016 US election. Democrats said the memo's release was a "shameful effort to discredit" the FBI and inquiries into Russian meddling. They warned that such action could trigger a "constitutional crisis not seen since the Nixon era", the BBC reported. The memo, written by Republicans, accused the FBI of abusing its powers.