Tester took in more than $1.9 million between April 1 and June 30, his highest total for a three-month span in the election cycle.
The campaign reports holding more than $3.6 million in Tester’s campaign war chest.
Rehberg has yet to report his figures.
“This grassroots campaign continues to gain momentum because Montanans know Jon is up against secretive, out-of-state special interests that are spending millions to buy votes for Congressman Dennis Rehberg,” Preston Elliott, Tester’s campaign chief, said.
Rehberg and Tester are buoyed by outside interest groups, which have spent nearly $6 million on the race so far.
Americans for Prosperity and Crossroads GPS, both Republican-backing organizations, are helping Rehberg. AFP held a “Tester Truth Tour” through Montana last month and is actively working at the Republican base against the first-term Democrat.
Crossroads GPS is spending its funds on issues ads, typically linking Tester to President Barack Obama, an unpopular figure among many Treasure State voters.