"In the second quarter, we raised over $600,000, a respectable fundraising effort for those of us in South Dakota. Our goal is to come close to that same number again in the third quarter," he told The Hill.

Rounds' second-quarter sum was much improved from his first-quarter haul of $184,000, and it helped to quiet some concerns that the establishment pick was failing to gain support and would struggle in his bid to replace Sen. Tim JohnsonTimothy (Tim) Peter JohnsonSenate GOP rejects Trump’s call to go big on gun legislation Court ruling could be game changer for Dems in Nevada Bank lobbyists counting down to Shelby’s exit MORE (D-S.D.), who plans to retire at the end of his term.

The seat is a top pickup opportunity for Republicans, but Rounds already faces three conservative challengers, and another looks likely to enter the fray soon. They're watching his third-quarter fundraising report to see if he manages to draw consistent support as his campaign develops.

South Dakota's media markets are relatively cheap and a successful Senate bid there isn't as costly as some other states. But Rounds said earlier this year that he plans to raise $9 million overall for his bid.

He'll need to step up his fundraising pace if he plans to hit that number by November of next year, however. He had raised just over $1.05 million for the cycle at the end of July.

At the end of the second quarter, Rounds had just over $750,000 cash on hand. He said he's looking to raise that sum to a million by the end of September.

"We'd love to have a million dollars in the bank and we're confident that we can make that happen," this quarter, he said.