US President Donald Trump on Tuesday attacked Tennessee Democratic Senate candidate Phil Bredesen at a rally for his opponent Marsha Blackburn.

Trump criticized Bredesen for being backed by national Democrats, including the Senate and House leaders.

Trump travelled to Nashville, Tennessee, as he steps up his efforts to stop Democrats aiming to regain control of the House or Senate - if not both.

"He's a tool of Chuck Schumer and of course the MS-13 lover Nancy Pelosi," Trump said of Bredesen during the rally.

Earlier this month, House Democratic Leader Pelosi criticized Trump's rhetoric and policies on immigrants after he called members of the international gang "animals."

Trump is using the campaign appearances to mobilize his core backers by highlighting his accomplishments in office, like improving economic indicators and moving the US embassy in Israel to Jerusalem, and resurrecting some of his go-to lines from the 2016 campaign.

He again said Mexico would fund a wall along the southern border.