President Trump's eldest son Donald Trump Jr. is preparing to hit the campaign trail for Republican candidates ahead of the November midterm elections.

A source close to Trump Jr. says he plans to hold rallies and fundraisers for Republicans, particularly in states and districts where the president's approval ratings are high.

Axios first reported on Trump Jr.'s plans.

Among Trump Jr.'s early targets ahead of the midterms are several Democratic senators up for reelection in states his father won in 2016: Sens. Joe Manchin (W.Va.), Jon Tester (Mont.), Claire McCaskill (Mo.) and Joe Donnelly (Ind.).

On Tuesday night, Trump Jr. called West Virginia Senate candidate Patrick Morrisey (R) to congratulate him on his primary election victory. West Virginia might be the first stop on Trump Jr.'s campaign tour.

"There are few people who have a more visceral connection with the GOP base than Don Jr. and he is going to be instrumental in helping to turn them out to vote in November," a source close to Trump Jr. told The Hill.

Trump Jr. is also adding to his staff ahead of the midterms push. GOP operative Andy Surabian has joined his team and will serve as a political adviser and communications strategist. Surabian is a Trump campaign veteran who also served in the White House as an aide to former chief strategist Stephen Bannon.