Vulnerable Sen. Mary LandrieuMary LandrieuYou want to recall John McCain? Good luck, it will be impossible CNN producer on new O'Keefe video: Voters are 'stupid,' Trump is 'crazy' CNN's Van Jones: O'Keefe Russia 'nothingburger' video 'a hoax' MORE (D-La.) bested her main GOP challenger in second quarter fundraising, raking in $2.1 million to Rep. Bill Cassidy's (R-La.) $1.6 million. 

The sizable haul was the Democrat's best quarter yet, and she still has more in the bank than Cassidy, ending June with $6.2 million cash on hand to the GOP congressman's $5.8 million, despite spending $3.39 million for the quarter. 

Cassidy's campaign did not release how much it spent in the second quarter, but it boasted that Cassidy has raised more money than any of Landrieu's previous challengers. In the first quarter of this year, Cassidy brought in $1.2 million compared to Landrieu's $1.8 million.

"People across our state are feeling the burden of Barack ObamaBarack Hussein ObamaAll five living former presidents to attend hurricane relief concert Overnight Health Care: Schumer calls for tying ObamaCare fix to children's health insurance | Puerto Rico's water woes worsen | Dems plead for nursing home residents' right to sue Interior moves to delay Obama’s methane leak rule MORE and Mary Landrieu's economy, but they are already voting with their pocket books because they know this election is an opportunity to stop Mary Landrieu's almost universal support for Barack Obama's crippling agenda," Cassidy said in a statement. "

Landrieu is one of the most vulnerable Democrats this cycle, suffering from low approval ratings for the president and ObamaCare in Louisiana. If no candidate wins 50 percent of the vote in November's all-party primary ballot, the top two candidates will face a December runoff. 

Cassidy is widely considered the GOP favorite in the race, but he faces a challenge from retired Air Force Colonel Rob Maness, who is running as the conservative alternative to the GOP establishment congressman. Maness has not yet released his second quarter fundraising numbers, but his campaign announced on June 23 that it had topped $1 million in contributions.

The other main Republican contender, Louisiana state Rep. Paul Hollis, withdrew from the race Monday.