(CNN) President Donald Trump's recent attacks on Sen. Jon Tester will be brought directly to Montana voters through a new online ad from the Senate Republicans' campaign arm.

The National Republican Senatorial Committee released a new ad Wednesday attacking Tester for airing charges that sunk Trump's nomination of Ronny Jackson for Veterans Affairs Secretary.

"What Jon Tester did to this man is a disgrace," Trump says in a portion of the speech cut for the ad. Trump also called for Tester to resign during a part of the speech not featured in the ad.

"Trump is right: it's time for Jon Tester to go," a narrator declares at the end of the ad.

The NRSC said the ad "will target voters statewide online and come as part of a significant investment from the committee."

Chris Meagher, the communications director for Tester's re-election campaign, responded to the ad, telling CNN, "Veterans across Montana want Tester to keep working to fix the VA so they get the better health care they were promised and earned. And that includes asking tough questions."

A Democratic aide responded to the ad saying that "it's laughable to think that Senate Republicans are going to be able to litigate this issue."

"What Montanans are learning and seeing and watching about this is Sen. Tester doing his job, making sure that someone who could be dangerous and harmful to veterans is not in position where he could hurt them," the aide said.

It's the latest salvo in what has become a heated fight between Tester, Trump, and Senate Republicans, who view his Senate seat -- in a state Trump won by 20 points in 2016 -- as one of the prime pick-up opportunities of the 2018 cycle.

Still, not all Republicans are on board with the attacks. Sen. Johnny Isakson, a Georgia Republican who chairs the Senate Veterans' Affairs Committee, declined to hit Tester, the top Democrat on the committee, for his role in the nomination fight.

"I'm not in the critiquing business," Isakson told Capitol Hill reporters Monday night.

Isakson defended Tester's decision to publicly release the allegations against Jackson, saying that "every senator has the right to exercise their options" and "that's the way it should be."

The feud began when Jackson's nomination for VA secretary fell apart last week, in part because of a series of allegations against Jackson, related to inappropriate workplace conduct and over-prescription , that Tester's office released last week. Jackson has denied the allegations.

Trump began attacking Tester in a series of tweets that covered Jackson's nomination as well as other issues like immigration

The Montana senate race is shaping up to be among the most competitive contests of the midterm elections. Already, super PACs from both sides have spent more than $1.5 million in the race.

The robust Republican senate primary there features three candidates -- Matt Rosendale, Troy Downing, and Russell Fagg -- who have hugged Trump closely in their bid for a shot to take on Tester in the fall.

Tester had a strong first quarter of fundraising, besting the combined haul of his three potential opponents with more than $2 million raised. The incumbent also has a cash-on-hand advantage, with more than $6.8 million banked.