The Louisiana senator announced his support on the Senate floor after Blanche's confirmation was thrown into doubt over opposition from two other Republican senators, Lisa Murkowski of Alaska and Susan Collins of Maine.
Cassidy said Blanche “is not perfect” but no one is, and he suggested another nominee may not be any better.
“I will vote for Mr. Blanche,” he said.
Blanche's path to confirmation has been complicated over a settlement of Trump's lawsuit against the Internal Revenue Service that has drawn intense scrutiny by Republicans and Democrats alike.
The settlement called for the creation of a $1.8 billion fund to compensate people who believe they were targetted by the Biden Justice Department because they were conservatives.
The Senate Judiciary Committee advanced Blanche's nomination only after a deal reached last weekend with two other Republican senators — John Cornyn of Texas and Thom Tillis of North Carolina — who had been threatening to block his confirmation over aspects of the settlement.
Under the deal, Blanche formally rescinded the “Anti-Weaponization Fund,” writing in an order that “there is no Fund.”
The Justice Department also clarified in writing that the tax audit immunity agreement applies only to claims open at the time of the settlement and does not protect Trump from examination of future tax filings. It also makes clear that only the parties that brought the lawsuit — Trump, two of his sons and the Trump Organization — are covered by the tax agreement.