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.
"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."
The Tester campaign did not immediately respond to a request for comment. 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.
Allegations made by Senator Jon Tester against Admiral/Doctor Ron Jackson are proving false. The Secret Service is unable to confirm (in fact they deny) any of the phony Democrat charges which have absolutely devastated the wonderful Jackson family. Tester should resign. The.....— Donald J. Trump (@realDonaldTrump) April 28, 2018
that covered Jackson's nomination as well as other issues like
....great people of Montana will not stand for this kind of slander when talking of a great human being. Admiral Jackson is the kind of man that those in Montana would most respect and admire, and now, for no reason whatsoever, his reputation has been shattered. Not fair, Tester!— Donald J. Trump (@realDonaldTrump) April 28, 2018
The migrant ‘caravan’ that is openly defying our border shows how weak & ineffective U.S. immigration laws are. Yet Democrats like Jon Tester continue to support the open borders agenda – Tester even voted to protect Sanctuary Cities. We need lawmakers who will put America First.— Donald J. Trump (@realDonaldTrump) April 30, 2018
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