Donald Trump on Monday launched a fresh attack on Attorney General Jeff Sessions, accusing him of jeopardising the chances of re-election for two Republican congressmen by bringing criminal charges against them just before the midterm elections.

The US president wrote on Twitter the Justice Department's decision to file charges will hurt safe Republican seats in the House of Representatives.

Election analysts believe there is a 50 per cent chance the Democratic Party will take control of the House, in which all 435 seats are up for grabs in the November 6 elections. Republicans currently hold a 236-193 advantage and there are six vacant seats.

"Two long running, Obama era, investigations of two very popular Republican Congressmen were brought to a well publicized charge, just ahead of the Mid-Terms, by the Jeff Sessions Justice Department," the Republican president wrote. "Two easy wins now in doubt because there is not enough time. Good job Jeff...."

Justice Department spokeswoman Sarah Isgur Flores declined to comment on Trump's tweets, which did not name the congressmen.